AGGLUTINATION ASSAYS

Abstract: A diagnostic system comprises a desk-top, flat-bed optical colour scanner (101) which scans a substrate, such as a microtitre plate (107) containing a mixture (105) of a sample and an agglutination reagent which react to generate an assay result of an agglutination assay. The scanner (101) generates a digitised image of the assay result. A personal computer (103) coupled to the scanner (101) is arranged to perform an analysis of the digital image to provide a quantified result for the degree of agglutination of the assay result.

Description: AGGLUTINATION ASSAYS The invention relates to apparatus and a method for analysing agglutination assays and in particular provides a diagnostic system usable in a laboratory or, especially, at the point-of-care, e.g. in a physician's office. Many diagnostic assays are available nowadays to physicians, and an increasing number do not require him to send the patient's sample (e.g. blood, urine, saliva, stool) to a diagnostic laboratory for analysis. Such in-office assays enable a result to be obtained rapidly and entered on to the patient ' s computer record by the physician or his assistant. One particularly useful form of assay is an agglutination assay in which a sample is mixed with one or more agglutination reagents. Bonding sites on the agglutination reagent (ε) bond to corresponding sites on components of the sample, if present, and this bonding results in agglutinates, which are visible clusters of bonded reagent and sample component. Thus, a desired reagent may be mixed with a sample and the presence of agglutinates in the mixture indicates the presence of the corresponding component in the sample. Traditionally, agglutination assays have been carried out qualitatively, with a judgment being made by the laboratory technician as to a positive or negative result. However, we have realised that a quantitative result can be obtained from an agglutination assay by analysis of the assay result to give a quantified result for the degree of agglutination, rather than a simple positive or negative result. Furthermore, we have now found that a quantified result can be obtained in a simple and straightforward fashion by the use of an imaging device (e.g a desk-top, flatbed optical computer scanner) capable of generating a digitised record of the image, i.e. the assay result, produced by an agglutination assay and of software capable of performing analysis of the digital image by manipulation (analysis) of the digitised record. Thus viewed from one aspect, the invention provides apparatus for the analysis of an agglutination assay comprising: an imaging device arranged to generate a digital image of an assay result comprising a mixture of a sample and at least one agglutination reagent; and data processing means arranged to process said digital image to generate a quantitative result representative of the degree of agglutination of the sample and reagent . According to the invention therefore a quantified result for the agglutination assay may be achieved simply and easily, and reflects the degree of agglutination rather than a simple yes/no result. Furthermore, the quantified result can easily be transferred to other data processing systems, for example to a patient data file for the patient providing the sample. Viewed from a further aspect, the invention provides a method for the analysis of an agglutination assay comprising the steps of: generating a digital image of an assay result comprising a mixture of a sample and at least one agglutination reagent; and processing said digital image to generate a quantitative result representative of the degree of agglutination of the sample and reagent. Preferably, the imaging device is a desk top, flat bed computer scanner, as this provides a low-cost imaging device which is readily available. More preferably, the data processing means comprises a personal computer, as this is again low-cost and readily available. The digital image may be a monochrome image. This would provide acceptable results for example in the case of agglutination assays involving white or light agglutinates imaged against a black or dark background. Preferably, the digital image is a digital colour image. In this way, greater flexibility is provided in distinguishing the agglutinates from the background. Furthermore, agglutinates of two or more different colours formed by two or more different agglutination reagents reacting with the same sample in the same assay result may be identified so that two tests may be carried out simultaneously. More generally therefore and, viewed from a yet further aspect, the invention provides a method for performing an agglutination assay comprising the steps of: providing a sample; providing at least two agglutination reagents, each having different optical properties; mixing the sample and the reagents to form an assay result; generating a digital image of the assay result; and processing said digital image by reference to the optical properties of each reagent to generate a quantitative result representative of the degree of agglutination of the sample and each reagent. The optical properties may be any suitable property, for example fluorescence, colour, degree of light scattering, shape, size or texture of the resultant agglutinates etc. Preferably, the optical properties are the colours of the reagents (or the resultant agglutinates) . The assay result will generally be formed in or on a substrate. A suitable substrate is for example a glass or plastics plate, such as a microscope slide or a microtitre plate, or similar substrate. Preferably, means are provided on the substrate to enclose the assay result within a defined area for ease of identification of the assay result in the digital image and to maintain a consistent depth of the assay result for a predetermined volume of sample and reagent (s) . Preferably, digital image data corresponding to the assay result within the digital image is located automatically, for example by a suitable arrangement of the data processing means. Generation of the quantitative result may involve determining at least one statistical characteristic of the distribution of pixels within the digital image. Suitable characteristics are mean pixel level, standard deviation, higher order statistical moments, autocorrelation, fourier spectrum, fractal signature, local information transform, grey level differencing etc. In one arrangement, generation of the quantitative result may involve determining the proportion of an area, preferably only the area of the assay result, of the digital image representative of agglutination products. Thus, for example, the background colour may be identified and the foreground colour (corresponding to the agglutinates) may also be identified and the proportion of the area of the image, or that region of the image corresponding to the assay result, being of the foreground colour may be calculated. Generation of the quantitative result may involve locating within the digital image clusters of contiguous pixels which are representative of agglutination products . Such clusters may be identified as groups of pixels having all their neighbouring pixels of the same, foreground, colour. The quantitative result may be generated by reference to the area, for example total area, of the clusters, the distribution of the clusters in the digital image or the number of the clusters in the digital image. The apparatus (system) of the invention may and preferably will be arranged to analyse assay results from a plurality (i.e. two or more) of different assays. The data processing means may be a personal computer. For example, a desk-top or lap-top (or palm top etc.) or other relatively inexpensive machine, e.g. of the type produced by Apple, Dell, Compaq, Olivetti, IBM and many others . Alternatively however a more powerful or extensive computer system may be used, especially where the system is located within a hospital or commercial organization (in which case the imaging device may be linked directly or indirectly, e.g. telephonically, to a component of a computer network) . Indeed even with "personal" computers the connection to the imaging device may be indirect, e.g. telephonic. The results generated by the system and method of the invention are preferably entered directly into the relevant patient ' s computer file, for example on the PC, or on a central computer to which the PC is linked by a network, or on a remote computer via a permanent or impermanent linkage (e.g. via the internet, etc.). In general, the system and method of the invention are intended primarily for use in the clinician's office/laboratory or in a hospital diagnostics laboratory and so direct entry into the patient's file on the PC itself or on a network- linked computer is of particular interest. The desk top scanner and/or the PC used in this system may be standard products available on the personal computer and computer accessories market. The scanner may operate in reflectance or transmission mode and in the latter instance may be a transparency (i.e. slide or dia) scanner or a transparency scanner add-on to a larger bed scanner. One example of a scanner that may be used is the Relisys Infinity or the Hewlett Packard ScanJet 6100C. This can be used to assign pixels to a grey scale or alternatively to assign a colour value (e.g. green, blue and red combinations) to each pixel. In order to use a transparent assay result with a standard, flat-bed scanner, an adapter may be used, for example, as shown in Figure 3. A suitable adapter 301 comprises two perpendicular, flat mirrored surfaces 302 which are placed over the assay result 303 on the scanner glass 305 such that they each make an angle of 45° with the scanner glass. Light 307 from the scanner passes vertically out through the glass (and thus through the assay result) and is reflected into a horizontal path by one mirror. The horizontal light is then reflected back towards the scanner glass by the second mirror. Thus, the scanner can detect an image of the light transmitted by the assay result in a position adjacent the assay result. The invention is not, however, limited to an arrangement comprising a flat-bed scanner and a personal computer. For example, a digital camera may be used to generate the required digital image data. Furthermore, a video camera arranged to generate digital image data, for example by means of a frame grabber, may be used. Each of these devices is readily available to the medical practitioner . In general, the imaging device will be arranged to scan the assay result under the illumination of daylight or a white light source. For example, in the case of a flat- bed scanner, white light is generated by the scanner itself. However, in the case of a digital camera or video camera, the white light source may be external to the imaging device and may be simply the ambient lighting in the medical practitioner's office. In such cases, where the light source is not controlled by the imaging device, it is advantageous for calibration to take place. Thus, the digital image data may comprise data corresponding to the colour composition of a calibration object of a predetermined colour or colour (ε) . The calibration object may be preεented to the imaging device together with the assay result or may be presented to the imaging device in a calibration step. In either case, it is possible for the data processing means to compare the digital image data relating to the calibration object with stored data relating to the predetermined colour (ε) of the calibration object and thereby determine a relationship between the colours and the digital image data. This relationship, which may be in the form of a look-up table or an algorithm, may then be used to translate the digital image data relating to the assay result into normalised digital image data that iε independent of the characteristics of the light source and the imaging device. The calibration object, or an additional calibration object, may also be used to calibrate the magnification of the imaging device. For example, the calibration object may be provided with a region of predetermined spatial dimensions from which the data processing means may calculate a relationship between the dimensions represented by the digital image data and the actual dimensions of the objects represented thereby. Alternatively, the imaging device may be maintained in a fixed spatial relationεhip with the plane in which the image result is or will be located. This is generally the case with a flat-bed scanner, but a suitable jig or the like may be provided for a digital camera or video camera . The system of the invention may be used in combination with appropriate photodetectors and/or illumination to quantify the properties of analytes exhibiting fluoreεcence and/or phoεphoreεcence. Analysis could also be carried out beyond the visible spectrum, for example in the infra-red or ultra-violet regions. Information found in grey-scale or colour imageε can be collected and stored to file in digitised form using flatbed scanners, digital cameras or video cameras. The bit-depth of the stored digitised file (standard bit- values: 1,4,8,15,32) will determine the amount of information that can be retrieved. The number of shades of grey or colour stored in these files are found as exponentials of 2 , i.e. bit-depth 1 (2 1 ) , 2(2 2 ), 3 (2 3 ) , 15 (2 5 of each of red, green and blue colour), 24 (2 8 of each of red, green and blue colour) . This means that 1, 4 and 8 bit files contains 2, 16 and 256 shades of grey respectively. Similarly a 15 bit file contains information about 32768 different colours (2 5 =32 different shades of each of the red, green and blue colour) , and 24 bit files information about 16777216 different colours (2 8 =256 different shades of each of the red, green and blue colour) . A bit depth of 32, possible to obtain even with simple flatbed scanners, makes it possible to store additional information of the colour intensities of each of the collected colours found in a 24 bit file. In more detail, this means that the last 8 bits are utilised for recording intensity, resulting in 256 different intensities (2 8 =256) for each of the 16777216 different colours stored. As a consequence of the information stored in the digitised files, quantitative measurement of colour is posεible. Uεing a 10 bit file, 1024 different shades of grey are available. A digitised image of a single spot of ink on white paper is measured aε a high intenεity black centre with edges along the rim composed of low intensity shades of light grey/ white. Thiε information can be preεented and visualised as a three-dimensional bell shaped surface with the third dimension expressed as intenεity of black. Integrating acroεε the surface gives the volume of the body covered by this surface. This volume can then be used as a direct quantitative measure when comparing different spots with different intensities. Similarly, using 15, 24 or 32 bit files it is also possible to derive quantitative information regarding the colour composition of the original image. Colour measurements and quantification measuring spots of either pure red, green or blue colour is easy and equivalent to the measurement performed using grey scale data. One way of doing this iε to tranεfer the recorded colour data by matrix calculations to hue-εaturation values (HS-values) . However, quantification of mixtures of colours are more complicated. The optical part of flatbed scanners contains three different detectors each with εpectral εensitivity to the three primary colours of light, i.e. red, green and blue, respectively. x(λ) has a high sensitivity in the red wavelength area, y(λ) in the green wavelength area and z (λ) in the blue wavelength area. The colours that we perceive and which are recorded are all the result of different x(λ), y(λ) and z (λ) proportions (stimuli) in the light received from an object. The resulting three values X, Y and Z being recorded are called tristimulus values. In thiε εystem every perceived and recorded colour can be expresεed with itε unique co-ordinate (X,Y,Z) in a co-ordinate εystem where the axes are formed by the three basic colours red, green and blue. Different numerical expressionε have been developed to express colour numerically. In a photometer/ reflectometer used in analytical chemistry to record colourε and intensity, monochromators or multiple εensors are used to measure the spectral reflectance of the object at each wavelength or in each narrow wavelength range. Simpler instruments, like flat bed scanners, as previously described measure colour by reflectance measurements only at the wavelengths corresponding to the three primary colours of light (red, green and blue) . The three different reflectance values recorded (tristimulus values) can then be used to convert the data to colour spaces like the "Yxy", "L * a * b" or the "L * c * h" systems. Digital cameras and video cameras are also capable of producing a digital output for each pixel in a digital colour image composed of the X, Y and Z values (RGB values) for that pixel. Thus, the output from such cameras may be used interchangeably with the output of a flat-bed scanner for the purposeε of the invention. Meaεurementε of mixtureε of different colourε using flat bed scanners or similar imaging deviceε result in multivariate syεtemε in termε of quantification of each of the colourε in the mixture . Colourε will be recorded as blends of each of the basic colours red, green and blue. A mixture of two different colours, e.g. red and blue, may be recorded as a new colour with its own intensity. In digitised form this colour will be determined by the relative amount of each of the two chromophores used and characterised by its tristimulus values (X,Y,Z), the basiε for all quantitative information εtored. To quantify the relative relationεhip between red and blue in a εpot compoεed of two colourε, information regarding the εpecific colour recorded for the mixture iε εufficient. Using flatbed scanners in colour mode and a sufficient bit depth of the digitised data, quantitative information can be achieved. However, to be able to perform the quantification of each of the colours in the mixture, standard solutions with known concentration must be uεed. Standards of two different colours and their mixtures can be εpotted on a white surface, measured and used to establiεh standard curves for the determination of the composition of an unknown colour spot composed of the same two colourε . The complexity of the quantification process measuring colours will vary depending upon the spectral characteristicε of the chromophoreε uεed. This is because only three different wavelength areas are used in the recording procesε uεing flat bed εcannerε. The possibility of separating different chromophores then depends upon the spectral separation of the different chromophores involved and their absorption maxima relative to the sensitivity of the x(λ), y(λ) and z (λ) detectors of the scanner. The basis for separating different chromophores is that the reflectance from each of the chromophores used (e.g. two or three) is different for at least one of these three wavelength areaε . For optimal chromophore systems, i.e. where the spectroscopic overlap at x(λ), y(λ) and z (λ) can be neglected, the corresponding X, Y or Z co-ordinate value can be used for their quantification. If chromophores with spectral overlap are used, all three values must be used as part of a multicomponent treatment of the recordings related to concentration. As an example, a blue and red chromophoric system with optimal spectral properties, the relative amount of red and blue chromophore can be calculated by measuring the average X/Z-ratio for every pixel in the recorded spot. By this way every mixture of these two chromophores can be recorded and estimated using a flat bed scanner or εimilar image acquiεition device. The relationεhip between the aεsay result and the colour image data may be stored in the form of a look-up table or an algorithm. In general, thiε relationship will be specific to a particular assay type and/or substrate. Thuε, for maximum flexibility, the data processing syεtem will have acceεε to a plurality of relationεhipε correεponding to the plurality of εubstrates that may require analysiε . These relationships may be stored locally to the data procesεing εystem or may be stored remotely, in which caεe the data processing εyεtem may acceεε the relationεhipε by meanε of a network or other communication channel . In the caεe of remote εtorage of the relationεhips, a database of relationships may be maintained and updated centrally, for example by the manufacturer of the asεay substrates. In this way, the latest analyεiε relationship will always be available to the medical practitioner. Advantageously, the data processing means of the invention is arranged to automatically identify the assay result within the digital image data and thereby locate the areas of interest in the image data. Thus, the assay result may be located in the digital image data according to the following method of analysing a digital image of a scene comprising at least one object, the object comprising at least one field, corresponding to the assay result. The method compriεeε : identifying the location of said object in said image; clasεifying said object; - identifying digital data corresponding to said field by reference to stored data relating to said claεεified object and the location of said object; converting said digital data to a corresponding quantitative result. The object, which may correspond to the substrate on or in which the assay result is contained, may be claεsified by geometric parameters, such as length, width, radius etc., by comparing identified parameters with corresponding geometric parameters for known objects . The subεtrate may be associated with a machine-readable identifier, for example a bar code, or similar machine- readable coding, the identifier including information relating to the assay type and preferably also the asεociated patient. Preferably, the identifier will be optically readable by the imaging device. However, it would alεo be poεεible for the identifier to be readable by a separate data acquisition device, for example a bar code scanner, magnetic strip reader, smart card reader or any device capable of converting data stored on the identifier to digital data which can be passed to the data procesεing εystem. In a simple form, the identifier may include a single number which corresponds to a record of a type of asεay or a particular patient in a databaεe accessible to the data proceεεing εyεtem. However, the identifier may contain more information, which may or may not be aεsociated with additional information available to the data proceεεing system. Agglutination reactions are valuable analytical tools which can be applied to many reaction systemε in which multivalent binding between reactants is posεible. Typical exampleε are immunoassayε which may be generally: - mixing polyclonal antibodies with a sample containing an antigen corresponding to the antibodies, and obεerving the formation of immunoagglutinates - mixing a monoclonal antibody with a sample containing an antigen carrying at least two antigenic functions (bivalent or multivalent antigen) and observing the formation of immunoagglutinateε mixing at leaεt two different monoclonal antibodieε with a εample containing a monovalent antigen and obεerving immunoagglutination any of the reactionε mentioned above, but applying the antibodieε coupled to particleε, such as latex particles, colloids, etc. any of the reactions mentioned above, but applied to antigens present on cell surfaceε in which case the number of antigens per physical unit is normally a hundred or more, and in which case such cells may be agglutinated by monoclonal antibodies even if each antigen molecule is monovalent. The reactionε are typically observed on the surface of a solid substrate such aε a glaεs or plastic plate, or in a solution in a microtitre plate. The solid surface is preferably coloured to contrast with the colour of the agglutinate . The formation of agglutinates iε dependent on the concentration of antigen in the sample. Thus, the more antigen present in the sample, the more frequent and larger the agglutinates. However, at a certain concentration level the antibodies will saturate the antigenic binding sites . When the number of antigen binding sites exceeds the number of antibody binding sites, the increase in agglutination will be correspondingly lesε pronounced and completely disappear at very high antigen levels. Thus, the level of reactants should be adjuεted to take this aspect into consideration. Agglutination reactionε may also be performed with any sets of molecules binding to each other, provided that each of the reactants has at least two binding sites each, or is coupled to a particle or otherwise linked together so that two or more binding sites per physical unit is created. Examples of other systems than antibodies/antigens that may form agglutinateε are (poly) carbohydrateε/lectinε, biotin or biotinylated compoundε/avidin or streptavidin, corresponding sequences of nucleic acids, any protein receptor and its corresponding ligand etc. Although the agglutination reactionε are, in fact, quantitative in nature, εuch that the level of agglutination correεponds to the presence of an analyte in a sample, the interpretation of the reεult iε traditionally merely qualitative. Since many of the analyteε which may be the εubject of such agglutination reactions are desired to be meaεured quantitatively, other and more complicated methods like ELISA, RIA, immunofiltration or immunochroraatography methods have been used. Agglutination-based productε for detection and quantitation of analyteε have been produced for a wide range of analyteε. Very early on, the field was developed using products for the detection of human chorionic gonadotropic hormone (HCG) in urine, for the diagnosiε of pregnancy. Two different principleε were used: 1. products were made with antibodies on a particle εurface, which gave agglutination in the preεence of the analyte; and 2. products were made with antigen on the surface of the particles, and reagent containing antibodieε waε added together with the test sample. In this second variant, agglutination took place in the absence or at low concentration of the analyte. However, a higher concentration of the analyte occupied the antibodieε and hindered the agglutination. Agglutination teεts for slides and visual inspections were made, and some companies, including Technicon, made autoanalyzers based upon instrumental measurements of particle inεpection by meaεurement of particle number and particle size. Furthermore, a long list of reagents for measurement of analytes by means of the measurement of alteration in turbidimetry as a function of the agglutination have been made. Automated spectrophotometers with a capacity for many hundred of testε per hour, e.g. Hitachi Instruments from Boehringer Mannheim in Germany and Cobas inεtrumentε from Roche in Switzerland, uses such reagents. These instruments, however, are very large and less convenient for patient- proximate testing and smaller laboratories and offices . Typical protein analytes for agglutination technology are C-reactive protein (CRP) , transferrin, albumin, pre- albumin, haptoglobin, immunoglobulin G, immunoglobulin M, immunoglobulin A, immunoglobulin E, apolipoproteinε, lipoproteinε, ferritin, thyroid stimulation hormone (TSH) and other proteinaceous hormones, coagulation factorε, plaεminogen, plasmin, fibrinogen, fibrin split products, tiεεue plaεminogen activator (TPA) , beta- microgobulinε, prostate-specific antigen (PSA) , collagen, cancer markers (e.g. CEA and alpha- foetoprotein) , several enzymes and markers for cell damage (e.g. myoglobin and troponin I and T) . Furthermore, agglutination reagents for testing for drugs, including prescription drugs and most illegal drugs, and many non-proteinaceous hormones, such as testosterone, progesterone, oestriol, have been made. Moreover, many agglutination test kits for infectious diseases have been made, including mononucleosis, streptococcus infection, staphylococcus infection, toxoplasma infection, trichomonas infection, syphilis. Such reagentε and reagent εetε are either baεed upon detection of the infectiouε agent itself, or detection of antibodies produced by the body as a reaction to the infectiouε diεeaεe. It should be noted, however, that the examples given above are not considered to be a complete listing of the applications of agglutination assays and many other applications are possible. Applying an imaging device, such as a flat bed scanner, to the reading of agglutination reactions will introduce a quantitative aspect to such reactions . The imaging device, e.g. flat bed scanner, may be applied to the measurement of simple contrast since agglutinates normally occur as white spots formed out of a transparent εolution. Such spots may be easily visualised or measured against a dark background. However, εuch direct agglutination iε less frequently used since the reactionε are not as easily controlled as when the antibodies are coupled to particles . In most caseε, white latex particleε are used, and the occurrence of white aggregates against a background of fully diεperεed white latex may be leεε eaεy to viεualise or read. Thus, colours are preferably applied to the particles . Colours are preferably chosen to facilitate the distinction between background and agglutinates . Another posεible aspect of this is to apply particles that change colour compared to the background when agglutinated. An example of such reactions is the agglutination of metal colloids. Most such colloids change colour upon agglutination, for example, colloidal gold iε reddiεh in itε original form, turning to blue when the agglutinateε exceed a certain εize, and further to black when the agglutinateε become even larger. Another poεεibility iε to mix particleε of two different colourε, for example blue and yellow particleε, of which only one type, εay the yellow particles, contain the antibodies. Thus, the unreacted solution will appear green while the introduction of an antigen will lead to the formation of yellow agglutinates towards a background changing from green to blue. A further posεibility is that of reading two or more reactions simultaneouεly . In the above example, if the blue and yellow particles are coupled to two different antibodies, respectively, each antibody being directed towards different antigens, the original green solution will form a mixture of yellow and blue aggregates if contacted with a solution containing both antigenε. A flat bed scanner may eaεily measure the occurrence of each type of aggregate, independently of each other, and thus provide a quantitative result for two simultaneouε reaction in one εingle reaction. Furthermore, such reactionε may of courεe be conducted with a plurality of differently coloured particleε, each containing antibodieε directed towards different antigens. The agglutination reactions should be performed either by mixing the sample and reagent (ε) on a flat surface and measuring the agglutination, or the reaction may be conducted in a test tube or a reaction chamber followed by pouring the reaction mixture to a surface after a certain time. The surface is preferably transparent in order to allow light from the flat bed scanner to interact with the reaction mixture. However, the εurface may alεo be coloured in a way that an optical filter iε created in order to facilitate reading of certain wavelength intervals of light . The surface may be εhaped so that the reaction mixture is encloεed within a distinct region in order to improve reproducibility in quantitative readings . This may be achieved by a circular elevation in a plastic surface which can be made according to standard production methods, or by the use of a microtitre plate. Furthermore, a device in which an agglutination reaction to be read by a flat bed scanner is performed, may conveniently also contain a cover which may be tilted over the reaction zone before reading. This will protect the flat bed scanner from being contaminated by the reaction mixture. Furthermore, such a cover may be coloured in order to form a proper background for optimal reading of the agglutination asεay. Some embodiments of the invention and some examples will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a εchematic digital image produced according to the invention; Figure 2 iε a εchematic diagram of a PC and εcanner arranged according to the invention; Figure 3 is a schematic view of an adapter used to enable a scanner to operate in a transmission mode,- Figure 4 is a flow chart showing a cluεter identification algorithm; Figure 5 shows the results of a transferrin agglutination aεsay analysed by a standard deviation method; Figure 6 shows the resultε of a transferrin agglutination assay analysed by a fractal signature method; Figure 7 shows the resultε of a tranεferrin agglutination aεεay analysed by a high pass method; Figure 8 shows the resultε of a tranεferrin agglutination aεεay analysed by a CLDM mean method; Figure 9 showε the results of a tranεferrin agglutination assay analysed by a CLDM energy method; Figure 10 shows the results of a transferrin agglutination asεay analyεed by a CLDM contrast method; Figure 11 shows the resultε of a tranεferrin agglutination aεεay analysed by a CLDM homogeneity method; Figure 12 showε the results of a transferrin agglutination asεay analysed by a standard deviation method; Figure 13 shows the results of a CRP agglutination asεay analyεed by a high paεε method; Figure 14 εhowε the reεults of a CRP agglutination assay analysed by a fractal signature method; and Figure 15 showε the reεults of a CRP agglutination aεεay analyεed by a CLDM mean method. Figure 1 εhowε εchematically an exemplary digital image 2 produced by a scanner in accordance with the invention. The image 2 correspondε to an arrangement of objectε 4 each of which contains one or more fields 6. In the following, such an arrangement of objectε 4 will be referred to as a "scene", the image 2 corresponding to the scene. Each of the objects may be, for example, a microscope slide or a microtitre plate or a similar flat substrate. The fields 6 within each object 4 are defined regions, where an asεay reεult iε expected to be located, for example the wellε of a microtitre plate. The εcene alεo compriεes a calibration object 8. The calibration object 8 is of a predetermined colour or colours, which colour or colourε are known to the data proceεsing syεtem for analyεing the image 2. Thuε, variationε in the ambient lighting conditions or in the senεitivity of the photodetectors of the scanner between the production of subεequent images 2 can be compensated with reference to the calibration object 8. Suitable predetermined colours for the calibration object 8 are a grey scale (all greys from 0% to 100%) each shade of which will contain equal proportions of red, green and blue. The calibration object may be divided into identifiable fields each of a different grey shade or other predetermined colour. In an alternative arrangement, the calibration object may be replaced or supplemented by one or more calibration fields on each object 4. Each object may also comprise an identification field 10, such aε a bar code or other εuitable machine- readable coding. The identification field 10 may contain information identifying the type of assay resultε in the fields, the senεitivity of the fieldε or other information relating to the object 4. The identification field 10 iε generally provided at a predetermined location on the object 4 such that it can be easily located in subsequent analysiε of the image 2 or used to define the accurate positions of the fields 6. The identification field 10 may be applied to the object 6 as part of the manufacturing process or may be applied once the assay has been carried out. In the former case, the identification field 10 may simply contain a serial number or a code (e.g. a bar code) by which the particular object may be identified during εubεequent use. Thuε, the data proceεsing system used to analyse the image 2, may contain information asεociated with thiε εerial number, and thus with the particular object 4. For example, the information may relate to the assay type, date and time of the assay etc. In the case of medical aεεayε, the information may include data identifying the patient, such as name, age, sex, symptoms etc. If the identifying field 10 is applied to the object 4 after manufacture, the field itself may be uεed to εtore the information deεcribed above, thereby obviating the need for additional dedicated data εtorage. When the scene contains a plurality of objects 4 the identification field 10 may be used to differentiate between the objects and ensure that the correct resultε are aεεociated with the correct object. In thiε way, the quantified assay result may be passed automatically to the correct patient file in a patient database. As haε previouεly been deεcribed, the data processing syεtem for analysing the image 2 may be a personal computer. An example of a suitable arrangement of a perεonal computer and εcanner iε εhown in Figure 2. Scanner 101 is connected to PC 103. In order to produce an image for analysiε, a predetermined volume of analyte and agglutination reagent iε mixed in a well of a microtitre plate 105 to form an assay result 107. The microtitre plate 105 is then placed on the scanner glass. The PC 103 is also connected to a bar code reader 109 for reading bar codes from patient records, substrates and analyte containers etc. The PC 103 has an optional data connection 111 to a remote computer for exporting quantified assay data. Referring back to Figure 1, the personal computer is provided with object data relating to the various types of objects 4 that it is required to analyse, including the calibration object 8. The object data will, in general, be supplied by the manufacturer of the objects 4 and will include, for each object: the geometrical dimensions of the object (e.g. width and height or for circular or elliptical objects radius or radii) together with the tolerances for those dimensions; the number, location on the object (with tolerances) and identification of the fields 6 provided on the object 4; and the location of the identification field 10. For each type of field 6, some of which may be provided on a number of objects 4, field data will also be provided including: an identification of the property that iε indicated by the field 6; and a description of the relationεhip between the degree of agglutination in the field 6 and the property indicated by the field. The relationεhip between the degree of agglutination of the field 6 and the property indicated by that field may be stored in the form of an algorithm, for example dependent on the mean and standard deviation of the distribution of agglutination products with the indicated property. Alternatively, the relationεhip may be εtored as a look-up table which maps the degree of agglutination of the field 6 on to the value of the property indicated by that field. The values stored in the look-up table may be determined empirically prior to the diεtribution of the objectε for general use. The image will generally be stored in 24 bit colour, i.e. 8 bits for each component colour, for example red, green and blue. Before analysiε of aεsay results can be undertaken, the scanner should be calibrated. Such a calibration may be undertaken before every analysis or may be undertaken on installation of the scanner. The first step in the calibration iε the production of an image corresponding to an empty scene, i.e. the scanner background which is preferably black. However, the background will not be perfectly black and dust or dirt deposits may result in blemishes on the background. The 24-bit empty image of an empty scene is converted to an 8 -bit grey scale image by adding together the 8-bit red, green and blue values for each pixel and dividing the sum by three. The mean grey εcale value is calculated for all pixels in the empty image. A grey threshold value is determined which iε equal to the calculated mean grey εcale value for the empty image plus a small offset, which may be, for example, a multiple or fraction of the εtandard deviation of the grey scale pixel distribution in the empty image. Thus, the grey threshold is deemed to be the value below which pixels may be considered to correspond to the scanner background. The positions of pixels with high grey values in the empty image are stored, these pixels being deemed to be due to dirt on the scanner background, and are deleted from all subsequent images, so that the image iε not diεtorted by theεe "dirty pixelε" . The second stage of the calibration is the calibration of colour reproduction of the imaging syεtem and the data processing syεtem uεing the calibration object 8. The calibration object 8 is identified as an object in the same way as objects to be analyεed (as iε described hereinafter) , but iε clasεified as the calibration object 8. The colours of the fields of the calibration object 8 determined by the data processing system are compared to the predetermined values for these colours, which are stored in the data processing εyεtem. On the basis of the differences in the determined colours and the expected colours, a calibration look-up table is calculated which maps the detected value of each colour component to its actual value. In the case of a flatbed scanner, initially an image 2 may be processed which contains only the calibration object 8,, so that the calibration look-up table can be constructed. As the variations in ambient light level will be insignificant for a flat bed scanner, there will be no need for re- calibration between subsequent images. However, the calibration object 8 can be included in every scene if variations in the light source or the εenεitivity of the photodetectors are expected. In this caεe the calibration object 8 will be identified initially by the data proceεεing εyεtem and the calibration look-up table will be constructed before the other objects 4 in the scene are processed. In the first stage of processing an 8 -bit grey image is created from the 24-bit colour image by summing the three 8-bit colour component (RGB) values for each pixel and dividing by three. Of course, the grey image may be created in any suitable manner, for example as a weighted average of the RGB values, rather than a simple average. Thiε grey image iε used in the identification of objects 4 and is not uεed in the analyεiε of the fields 6, where the 24 bit colour image is used. The dirty pixels identified in the calibration stage are removed from the image 2 by replacing their grey value with the mean value of their neighbouring pixels . The RGB values of the dirty pixels in the colour image are also respectively replaced by the mean RGB values of their pixels neighbouring the dirty pixel. This may be done before the grey image is created. The background in the grey image is removed by setting to zero the value of each pixel which has a detected grey value below the threshold calculated during the calibration stage. Subsequently, unwanted gaps in the image are removed by operating on the grey image with a maximum operator and then with a minimum operator. A maximum operator is a matrix of n by n pixels, the function of which is to replace the central pixel of the matrix with the highest pixel value occurring within the n by n matrix. Similarly, a minimum operator replaces the central pixel of the matrix with the lowest value found therein. Each pixel of the grey image is operated on as the central pixel of the maximum/minimum operator. The size n of the operators is determined by the objects that are to be analysed. Objects that contain very dark regions (gaps) extending from one boundary to the other, or at least very close to the boundaries, will be considered as two objects by the data proceεεing system as the gap will be indistinguishable from the background. Thus, by removing such gaps from the grey image it will be ensured that the objects are correctly identified by the data procesεing εyεtem. The gapε are not removed from the colour image, however. Thuε the maximum gap εize g to be removed from a particular image iε the largeεt gap appearing in any of the objectε in the image. The operator size n is equal to the maximum gap size g (in metreε) multiplied by the resolution of the image (in pixels per metre) . The maximum gap size g for each object is part of the object data stored in the data processing system for each object 4. The maximum gap size for a particular image 2 is the maximum gap size g for all objects which can appear in the scene. Thus, this may be the maximum gap size for the entire list of objects 4 εtored in the data proceεsing syεtem or for a selected list of objects that has been defined by the operator as expected to be detected in the scene. Once the dirty pixels, background and gaps have been removed in the pre-procesεing εtage, the contourε of each object 4 in the grey image are traced. Any objects having a boundary less than a predetermined threεhold are deleted as being of no interest. Thiε threshold may be determined with reference to the list of all objects stored in the data procesεing systemε or a user-defined list of all objects that are expected to appear in the scene. When the boundary of each object has been determined, the centre of the object is calculated and the principal axeε (x, y εhown in Figure 1) of the object 4 are determined. If, from the boundary, it iε determined that the object iε circular, any two perpendicular axeε coincident at the centre of the object are choεen. If it is determined that the object is square or rectangular, axes x, y are chosen perpendicular to the sideε of the object 4. In this way, a coordinate system is establiεhed for each object of interest with the origin of the coordinate syεtem at the centre of the object. The length and width (or radius) of the object have also been determined from the boundary, so that the object can be claεεified by comparison of these parameters with the stored object data. If the object meets the criteria of more than one set of stored data, further features, such as field positions, of the object are identified and compared to stored data. The object is classified as the stored object type which it most closely matches, within an acceptable error range. If the object does not match the parameters for any of the object data, it is classified aε an unknown object. The location of the fieldε within the claεsified object are known from the data stored in the data processing system in terms of the local coordinate system that has been determined. A complete set of data has now been created from the 8 bit grey image, which data identifies each object in the grey image (and thus in the colour image) and the exact location of each field (including the identification field 10) in that object. Thus, from the 24-bit colour image the RGB values for each field 6 of each object 4 can be retrieved. These RGB values can be converted to device-independent colour values using the calibration look-up table. In addition, the information from the identifying field 10 of each object can be read and associated with the assay values which will be calculated for that object. All identifying and assay data is in electronic form and therefore can be passed easily to a, for example patient, database or similar internal or external data syεtem for aεsociation with other data relating to the aεεay, such as demographic or treatment data. As will be εeen from the above, a flat bed εcanner can be used simply to obtain accurate assay information from an asεay object. The image may be εtored in a device- independent format εo that it may be processed at a remote location or archived for future reference. For cleanlinesε and ease of handling, the objects may be placed on or in a window, holder or adapter, which may advantageously locate the object on the scanner. However, the above processing methodology allows for the use of other data acquisition meanε, aε there iε no requirement for the accurate poεitioning or lighting of the objectε. Hitherto, complex deviceε εuch aε spectrophotometers have been used to ensure the accurate location of assay fields and the accurate reproduction of the colour of such fieldε. However, in accordance with the invention, accessible and relatively inexpensive digitisation equipment can be used to obtain the initial image data, which is then processed by the data proceεεing εystem to obtain the aεεay reεults. Thuε, aε an alternative to a flat-bed εcanner, a digital camera may be uεed to obtain the image data. In this case, the objectε to be analyεed are placed on a εurface above which the camera is poεitioned. The εcene iε photographed by the digital camera to produce the digital image. The image may then be processed in the εame way as for the image obtained by the scanner. However, in order to obtain accurate identification of the size of each object, data relating to the height of the camera above the surface and the camera angle may need to be made available to the data procesεing system. In addition, a calibration object may be required in each scene aε the resultant image may be affected by ambient lighting conditions. The calibration object may alεo contain εpatial calibration information such as one or more regionε of predetermined dimensions. Similarly, as an alternative to the scanner or digital camera, a video camera and a frame grabber may be used to produce the digital image data. An advantage of a digital camera or video camera over a flat-bed scanner is that the substrate may be located in the view of the camera without physical contact therebetween. In the case of a flat-bed scanner, the asεay εubεtrate iε placed on the scanner glasε and thuε deposits, such as urine, faeceε or blood, from the εubεtrate may be transferred to the glasε. However, a camera may be positioned at a distance from the substrate, for example above the subεtrate, and may accurately generate digital colour image data of the εubεtrate without contacting the substrate. Using, for example, a Cinet, 32MB RAM, 166 MHz Pentium processor PC coupled to a Hewlett Packard ScanJet 5p colour scanner, the procesε of the invention may be performed using the following steps: (A) The "scene" is configured (B) The scan of the scene iε performed (C) The scene is segmented into "regions" (D) The regionε are identified (E) The "quality" of the regions is checked (F) Data values determined are asεociated with patient identifier information (G) The data is exported to a central computer and into the appropriate patient file. In step (A) , if appropriate, the operator will set a scan delay (e.g. 60 or 120 seconds) and select whether the substrate is to be scanned once or more than once, e.g. twice or more. The scan delay will generally cause appropriate prompt signalε, e.g. audible beeps, to occur at pre-set delay times before the scan is performed. Thiε allowε the operator to effect the aεεay by mixing the εample and the agglutination reagen (ε) and place the εubstrate on the εcanner bed εo that the scanning takes place at the desired time after the asεay commences. This is important as many asεay results must be read at a particular time after assay commencement. Where multiple substrates are to be read by the scanner, these will preferably be spaced apart on the scanner bed such that they are read by the scanner at the same time delay after the sample and reagent have been mixed. To assist in this, a mask may be placed on the scanner bed showing the operator where to place the εubstrate or εubstrates . Multiple scans will be selected where it is desirable to follow the progresε with time of the aεεay result, e.g. to report the peak value or to report the change in value over a specific time period. Multiple scanε will alεo be εelected where the substrate is arranged for a multiple assay, i.e. to provide values for more than one parameter characteristic . For example by having different agglutination reagents in different wells of a microtitre plate, where the individual asεays involved require different development times . Because the assays may require specific development times, it is preferred in the methods of the invention to use reading deviceε (e.g. scanners) which have uniform start-up times, i.e. which will read the subεtrate with the εame time delay after inεtruction each time. For thiε reaεon, the HP ScanJet 5p has been found to be a preferred flat-bed scanner. In step (A) , the operator will generally also select the area to be scanned and select whether bar codes (or other machine readable codes) are allowed and optionally he will also select which such codes are allowed. Moreover the operator may select whether or not a prompt signal is required and the timing and type of such a signal (e.g. audible or visible). If bar codes are allowed, the data handling operation will involve identification of the bar code or codes associated with the subεtrate or εubstrates. This may for example serve to identify the patient and/or the nature of the subεtrate and hence the assay or asεays involved. A patient bar-code may conveniently be provided on a tear-off portion of the label for the sample-container for the test substance. Such a tear- off portion can be attached to the subεtrate before εcanning or placed adjacent to the substrate on the scanner bed. The substrate itself will preferably carry a code identifying "the nature of the assay. The PC will conveniently be set up to offer the operator a list of assays which it can analyse and from which to select the asεayε the operator iε uεing. For the operator 'ε convenience, where multiple substrates are being scanned, the operator will conveniently be able to εpecify whether all substrates derive from the same patient, whether all substrateε are the same (i.e. perform the same asεayε) , or whether a mixture of εubεtrateε iε being εcanned. Either before or after εcanning, the operator will conveniently be prompted to identify the patient, e.g. by providing a code permitting the results to be exported to the patient ' s data file. With this input from the operator the scanning may proceed. If a prompt signal has been selected, the operator will wait for the prompt, mix the first sample (ε) and reagent (ε) in the first subεtrate on receiving the prompt and then place the εubεtrate on the εcanner bed in the aεεigned poεition after the required contact time, mix the second sample(s) and reagent (ε) on receiving the next prompt, etc. until the scanner bed is fully loaded. After the predetermined period (s) from the first prompt the scanner will perform the first and any subsequent scans and export the image data to the PC. The subεequent image data handling by the PC can be effected in many wayε and that described hereafter is simply a preferred scheme. (1) Find gap size (2) Make a binary or gray image (3) Find the "active" image (4) Remove noise (5) Run maximum operator in a first (x) direction (6) Run maximum operator in a second orthogonal (y) direction (7) Run minimum operator in x-direction (8) Run minimum operator in y-direction (It is poεεible to configure the εcene to require the maximum and minimum operatorε to be run in one direction only. Thiε εaveε time but restricts the location of objects . ) Gap size for the subεtrates is εpecified by the operator's identification of the nature of the subεtrate in step (A) . The PC takes the image data and segments the scene into regions. For each pixel of the colour image, the colour black is assigned if the mean value of the R, G and B values ((R+G+B)/3) is below a first threshold and the difference between the highest and lowest R, G or B valueε iε not greater than a second threshold value. This produces a treated colour image and from thiε a grey εcale image iε created uεing the mean R, G, B valueε now aεsigned to the individual pixels. For example this may be achieved by εcanning an empty image, i.e. a clean and empty εcanner bed, and setting the first threshold as the mean (R+G+B)/3 value for this empty image plus a pre-set value. The second threshold may be set as the product of a pre-set coefficient and the average value of the difference for the R, G and B values from the R, G and B values for the empty image. In other words, a pixel is not discarded if its average (R+G+B)/3 value is below the first threshold but one or two of its R, G and B valueε are individually noticeably higher than the reεpective "background" R, G or B value. From thiε grey image, the active area, the area containing the substrateε and/or bar codes, is selected by moving inwards from the image edges until the number of non-black pixels exceeds a preset limit. The noise may be removed by setting a noise size as half the gap size and removing all structures smaller than the noise size, i.e. setting to black all pixelε in such structures . This reduceε the poεεibility of a noiεe pixel being included in an object boundary. Gaps are then removed by operating on the image with a maximum operator followed by a minimum operator. The maximum operator is as wide as the largest gap size for the objects (εubεtrateε) allowed in the εcene. Of course, if the largest gap size is zero this operation is not required. The objects in the image are then located by finding a non-black pixel with an adjacent black pixel (i.e. a border pixel) and following the path of adjacent such non-black pixels until the original is returned to. From the reεultant liεt of border pixelε, for each region the centre is calculated and the geometry is determined, e.g. as a rectangle or circle. Travelling from the centre of each region to its borders along its principal axes, the length and width of the region is calculated. Each εuch region found by thiε segmentation step is then clasεified aε an object or an unknown. The border data for the unknownε are combined to create regionε which are claεεifiable aε objectε. For each object the length and width are compared with the length and width data of allowed objectε (from the databaεe εtored by the PC which containε the characteriεtic data for the substrates it is εet up to read) . A quality factor iε then determined for the orientation of each object and the orientation iε selected as being that with the lowest (i.e. best) quality factor. For each object, the quality factors for all objectε it iε allowed to be is determined and the object is identified as being that with the lowest quality factor. For each field in the object (located using the data for the allowable objects in the PC's object database mentioned above) , the field centre is located. The position of the field is then fine-tuned by calculating for each R, G and B image the standard deviation for its fit to the allowable object when moved small distanceε Δx and Δy and εelecting the poεition at which the εtandard deviation is minimised. For pixel calibration, one may use a εtandard colour card to conεtruct a table for RGB values . Using the same colour card the same table should be constructed for the particular εcanner being uεed, the colour space should be divided (e.g. mapped onto a 16x16x16 cube space) , and each calculated or calibration point may be assigned into one such division (cube) . For more precision, corrected positionε of such points within each division may be interpolated from the values of the division corners (i.e. the corners of one of the 16 3 cubes making up the colour space) . Once the fields have been located in the digital image, the pixels of each field are analysed to obtain a quantified result for that field. For fields representative of an assay result in which agglutinates of one colour appear as foreground against a background colour of the agglutination mixture, each pixel is asεigned to either the group of foreground pixels or background pixels. This is done by calculating the distance Db, Df of the RGB colour vector x of each pixel in RGB colour space from a predetermined mean background vector μb or mean foreground vector μf . The distances are calculated using the following formulae : Db = (trans (x-μb) )* (Inv(∑b) )* (x-μb) Df = (tranε (x-μf) )* (Inv(∑f) )* (x-μf) where ∑ represents the covariance matrix, defined as: ∑b = E{ (x-μb)* (trans (x-μb) ) } and E is the expectation operator, trans is the transpoεe operator and Inv iε the invert operator. Thus, if for a particular pixel Df<Db the pixel is clasεified aε a foreground pixel, i.e. the pixel represents an agglutinate, and if Df>Db the pixel is classified aε a background pixel. Next, the pixels are classified into sub-groups of each of the foreground and background groups, where each subgroup represents a cluster of connected pixels. A cluster iε defined aε a group of pixelε, where it is poεεible to move from one pixel in the group to any other without moving outside the group. The clusters are located from the group of foreground (or background) pixels using the algorithm shown in Figure 4. According to thiε algorithm, pixels are selected sequentially from the group P of all foreground pixelε . One pixel iε εelected from P and made the initial member of a new group newG. A group B of all 8 pixelε which neighbour the εelected pixel is created. Thus, if the selected pixel is (i,j) in Cartesian spatial co-ordinates, the neighbouring pixels are (i-l,j-l), (i,j-l), (i+l,j-l), (i-l,j), (i+l,j), (i-l,j+l), (i,j+l) and (i+l,j+l). A first pixel x is selected from group B and then removed from that group. If x is a foreground pixel it iε added to group newG. The 8 pixels neighbouring pixel x are then examined sequentially and any that are not already members of group B or group newG are added to group B . Thus, group B representε the group of pixels bordering the pixelε of group newG and group newG iε expanded by adding pixels from B if these pixelε are foreground pixels. Eventually, group B will be empty because on the previouε examination, the only additional neighbouring pixelε were background pixelε. At thiε point, it iε known that group newG iε surrounded by background pixels. Thuε, group newG is added to the list of cluεters and the pixels contained in group newG are removed from group P aε it is now known that these pixels are members of cluster newG. The algorithm stops when group P is empty, i.e. all pixels have been classified into clusters. Properties of the digital image and thus of the aεεay result can be calculated from the characteristics of the clusterε. Suitable characteriεticε are: total area, i.e. number of pixelε, of foreground or background; total area of foreground or background including only those clusterε including more pixelε than a threεhold value; mean cluεter area, i.e. total area divided by number of cluεterε; mean cluεter area for cluεterε larger than a predetermined threεhold; mean diεtance between centreε of clusterε, uεing the εmallest of the distances from a first cluster to each of the other clusterε aε the diεtance for that cluεter; mean distance between clusterε exceeding a predetermined εize; number of cluεterε ; and number of clusters exceeding a predetermined size; or any combination of the above. The above processing scheme can be applied to assay results generating more than one agglutinate type with each agglutinate type being of a different colour. In this case, a plurality of foreground colourε, one correεponding to each agglutinate type are uεed and pixelε are grouped aε background or one of the foreground colours using a corresponding method to the above . Other characteristicε of the digital image, for example deεcriptive of the texture of the image, may be used to derive the quantified result, either with or without classifying the image into clusterε. For example, these characteriεticε may include: Standard deviation Mean Higher order εtatiεtical moments Autocorrelation as described in Milan Sonka et al . , Imaging Procesεing, Analysis and Machine Vision Chapman & Hall, 1993 Fourier εpectrum as described in Milan Sonka et al . , Imaging Proceεsing, Analysis and Machine Vision Chapman & Hall, 1993 Fractal signature as described in F. Albregεten, Fractal Texture Signature Eεtimated by Multiscale LIT-SNN and MAX-MIN operators on LANDSAT-5 MSS Images of the Antartic Proceedings, 6th SCIA, pp. 995-1002, Oulo Finland, June 19-22, 1989 LIT (local information transform) aε described in R.M. Haralick, Statistical Image Texture Analysis, In Handbook of Pattern Recognition and Image Processing, Academic Press, 1986 GLDM (gray level difference method) as described in R.M. Haralick, Statiεtical Image Texture Analysis, In Handbook of Pattern Recognition and Image Procesεing, Academic Preεε, 1986. Theεe propertieε may be calculated from the red, green or blue components of the pixels or from a combination of two or more of these. The chemical properties indicated by the assay result can then be calculated either by comparison with empirically derived data and interpolation or by an algorithm. The PC at this stage should prompt the operator to identify the patient from whom the samples derive if thiε information haε not already been supplied. This could be input manually, but desirably the PC will be linked to a bar code reader, such as an Opticon ELT 1000 wedge reader, so that patient codes may be read in from sample container labels. The data can at thiε εtage be exported, e.g. to the patient's physician' ε database or a central hospital computer. A preferred export format is the American Society for Testing and Materialε (ASTM) format. EXAMPLE 1 An Avitex-CRP teεt kit from Omega Diagnoεticε Ltd, of Alloa, Scotland waε used. The test kit contains white latex particles coated with antibodies to CRP, a positive and a negative control. The test is normally performed by application of one drop of latex suεpension on a black plastic teεt slide, followed by one drop of sample (either patient serum or control) , stirring with a wooden stirrer for two minutes, and inεpecting the plate for viεible aggregateε . We performed the teεt in a microtitre plate by mixing 25 microlitre latex suspenεion with 25 microlitre εample, followed by gentle εtirring for two minutes. The microtitre plate was covered by a black plastic sheet and scanned in a Hewlett Packard Scan Jet 6100 C scanner connected to a PC. The samples tested were a dilution serieε of the poεitive control encloεed with the kit. The εcanner automatically identified the wellε in the microtitre- plate where the reactionε had occurred, and calculated the average Standard Deviation (SD) of the colourε red, green and blue in an area of 3 x 3 mm about the centre of each well. The reεultε obtained where as follows: SE Visual appearance Undiluted (100%) 11. .0 Large aggregates Diluted 4+1 (80%) 9. .1 Clearly visible aggregates Diluted 3+2 (60%) 6, .5 Viεible aggregateε Diluted 2+3 (40%) 3 .0 Faintly viεible aggregates Diluted 1+4 (20%) 3 .0 No aggregates Negative control 3 .0 No aggregates A value of CRP is not stated for the positive control. However, the detection limit for the kit is stated to be 6 mg/L which seems to be between 30 and 40% dilution of the control. Thus, the control appearε to be about 20 mg/L. EXAMPLE 2 To coat particleε with antibodieε, a 1 ml εuspension containing 5.7% particles of amino-subεtituted, white polyεtyrene particleε of average diameter 0.23 μm, available from Bangs Laboratories Inc. of Indiana, USA, was subjected to buffer change in a hollow fibre unit resulting in a final compoεition of 5% particleε in 0.1 mol/1 εodium borate buffer (pH 8.0) containing 0.02% NaN 3 . To 1 ml of the suspension was added 20 μl of a solution containing about 2 mg/ml of rabbit polyclonal antibodies to human transferrin and incubated at 20°C under end-over-end mixing for about 18 hours. The suεpenεion waε thereafter εubjected to centrifugation sufficient to collect the particles in a pellet in a test tube, and free binding sites in the particles were blocked by resuspension in 1 ml 0.1 mol/1 sodium borate buffer (pH 8.0) containing 0.033% human serum albumin and 0.02% NaN 3 (blocking medium), and incubation for two hours at 20°C. Thereafter, the suspension was subjected to two cycles of centrifugation sufficient to collect the particles in a pellet, and resuspension in 1 ml of O.lmol/1 Tris-HCl-buffer (pH 7.4) containing 0.33% human serum albumin and 0.02% NaN 3 (washing medium) and centrifugation. Finally, the particleε were εuspended in 1 ml of the washing medium. The standard serum Seronorm available from Nycomed Phar a of Oεlo, Norway, containing 2.7 g/1 Tranεferrin was diluted with 0.154 mol/1 NaCI to yield a serieε of solutions containing 10, 20 and 40 mg/1 of Transferrin, respectively. In addition, a blank containing no Transferrin was included. The agglutination reaction was carried out as follows . 25 μl of the latex suspension was mixed with 25 μl of one of the Transferrin εolutionε on a horizontally poεitioned tranεparent plexiglass plate visualiεed against a dark, underlying surface, and mixed by circular rotationε with a wooden εtick to εmear out the mixture over a circular surface with a diameter of about 1.5 cm. After about five minutes, viεible agglutination took place in the solutions, except for the blank. Visual inspection of the agglutinates gave the following resultε : The plexiglasε plate waε transferred to a Hewlett Packard ScanJet 6100c scanner and scanned at a resolution of 150 dpi. The pictures obtained were then subjected to the following numerical analysis methods (described in detail below) within a defined area of each agglutination pattern obtained: Trimmed mean method, with variations in the High and Low exclusion limits (results not shown) ; Standard deviation method, with variationε in the filter εize and the High and Low exclusion limits (Figure 5) ; - Fractal Signature method, with variations in the filter sizeε and the High and Low excluεion limitε (Figure 6) ; High paεε method, with variations in the filter sizeε and the High and Low excluεion limits (Figure 7) ; and Colour Level Difference Method (CLDM) method, with variations in the filter size and the High and Low exclusion limitε, and taking the CLDM mean (Figure 8) , CLDM energy (Figure 9) , CLDM contrast (Figure 10) , and the CLDM homogeneity (Figure 11) . The resultε obtained applying an optimal combination of the variable parameters are shown in Figures 5 to 11. The curves clearly demonstrate a dose-dependent relationship illustrating that the agglutination reactionε can be read quantitatively by applying a εcanner and a εuitable set of algorithms, whereas such reactions can only be read as a simple, qualitative yes/no-reaction by the prior method of visual inspection. When the data are analysed by the Standard Deviation method, fairly linear dose response relationships are achieved over a range of filter sizes and exclusion limits. Thus, thiε method appearε to be well-suited for analysiε of a test with the present chemistry profile. Applying data analyseε by the Fractal Signature method demonstrates that the exclusion limitε are of minor importance, and that similar dose response curves may be achieved with various combinations of filter sizes . The curve profiles are almost linear in the lower concentration range, and then level out. Thus, data analysis by Fractal Signatures can be suitable where analysiε should be weighted to the lower part of the curve, and the upper parts play a lesε εignificant role. The oppoεite concluεion iε reached when the High Paεs analysis method is applied. The method gives less ability to discriminate in the lower range, and is fairly linear in the upper. Thuε, thiε method may be uεeful if a certain cut-off concentration iε enviεaged. The reεultε are improved when lower excluεion limitε are choεen. Applying CLDM Mean to the analyεiε of the data giveε a εigmoid doεe reεponεe relationεhip and iε thus weighted towards the middle part of the curve . The method requires rather low filter values, and is then leεε dependent on the exclusion limitε. A εimilar concluεion may be drawn from application of CLDM Energy and CLDM Homogeneity. The curve iε sigmoid, and is best achieved at lower filter values. The dose-responεe relationεhip iε negative. Application of CLDM Contrast to the data analysis gives results resembling the High Pasε method: Less ability to discriminate in the lower range, and an increasing dose reεponεe in the upper part. Thus, this method may also be suited if a certain cut-off value iε desired. The overall data demonstrate that agglutination may be measured by a obtaining a digital image using a scanner, and application of the resulting images to various mathematical/εtatiεtical analyεiε to arrive at a method that quantifieε the reεult. The method of mathematical/εtatiεtical analysis may be selected to suit the particular features of the agglutination assay in question. EXAMPLE 3 To coat the particles with antibodies, a 1 ml suspenεion containing 5.7% particleε of amino-substituted polystyrene particles of average diameter 0.23 μm, available from Bangs Laboratories Inc. of Indiana, USA, was εubjected to buffer change in a hollow fibre unit, reεulting in a final composition of 5% particles in 0.1 mol/1 sodium borate buffer (pH 8.0) containing 0.02% NaN 3 . To the suεpension was added 70μg of each of two anti-C-reactive protein (CRP) monoclonal antibodies (6405 and 6404 available from Medix Biochemica, Helsinki, Finland) and the suspension was then incubated at 20°C under end-over-end mixing for about 18 hours. The εuspension waε thereafter εubjected to centrifugation sufficient to collect the particles in a pellet in a test tube, and free binding εites in the particles were blocked by resuspension in 1 ml 0.1 mol/1 sodium borate buffer (pH 8.0) containing 0.033% human serum albumin and 0.02% NaN 3 (blocking medium), and incubation for two hourε at 20°C. Thereafter, the εuεpenεion waε εubjected to two cycleε of centrifugation sufficient to collect the particles in a pellet, and resuεpenεion in 1 ml of O.lmol/1 Triε-HCl-buffer (pH 7.4) containing 0.33% human serum albumin and 0.02% NaN 3 (washing medium) and centrifugation. Finally, the particles were suεpended in 1 ml of the washing medium. 8 μl of a solution of 25 mg/ml of human C-reactive protein (CRP) , available from ICN Pharmaceuticals Inc. of California, USA, was added to 250 μl washing buffer to form a solution of 100 mg/1 CRP. The solution was diluted in a serieε forming concentrationε of 75, 50, 25, and 12.5 mg/ml CRP, respectively. 25 μl of the latex suεpenεion waε mixed with 25 μl of one of the CRP εolutionε on a horizontally poεitioned tranεparent plexiglaεε plate visualised againεt a dark, underlying εurface, and mixed by circular rotationε with a wooden εtick to smear out the mixture over a circular surface with a diameter of about 1.5 cm. After about five minutes, visible agglutination took place in the solutions containing the highest concentrations of CRP. Visual inspection of the agglutinates gave the following reεultε : The plexiglasε plate waε transferred to a Hewlett Packard ScanJet 6100c scanner and scanned at a resolution of 300 dpi. The digital images obtained were then εubjected to the following numerical analyεiε methodε within a defined area of each agglutination pattern: Standard Deviation method, with variations in the filter size and the High and Low exclusion limitε (Figure 12) ; High Pasε method, with variationε in the filter sizes and the High and Low exclusion limits (Figure 13) ; Fractal Signature method, with variations in the filter sizes and the High and Low exclusion limitε (Figure 14) ; and Colour Level Difference Method (CLDM) method, with variationε in the filter εize and the High and Low excluεion limitε, and taking the CLDM mean (Figure 15) , CLDM energy (not shown) , CLDM contrast (not shown) , and the CLDM homogeneity (not shown) . The reεultε obtained applying an optimal combination of the variable parameterε are εhown in Figureε 12 to 15. The curveε clearly demonεtrate that a dose-dependent relationship may be found by analyseε of the pictures with the standard deviation, fractal signatures, high pass, and colour level difference mean methodε . Suitable dose-response curves where found for certain sets of parameters illustrating that the agglutination reactions can be read quantitatively using a scanner and a suitable set of algorithms . Such reactions can only be read as simple, qualitative yes/no-reactionε by the known method of viεual inspection. The Standard Deviation method resultε in a εlightly εigmoid curve, but is reasonably suited for application over the entire range measured. The Fractal Signature method weights preciεion in the lower part of the concentrationε meaεured, whereaε the High Pass method weights precision in the upper part of the concentrations . The CLDM Mean forms a sigmoid curve weighting the middle part of the curve. In thiε particular experiment, CLDM Energy, Contraεt and Homogeneity (curveε not εhown) were leεε suited because they demonstrated small variation between the two lower, and the three upper CRP-values, respectively. STATISTICA /MATHEMATICAL ANALYSIS METHODS The following methods were used to analyse the digital image of the agglutination assay generated by the εcanner. In the description of each method, the variable I(x,y) (=R(x,y), G(x,y) or B(x,y)) represents the image array of red, green or blue pixel valueε (0- 255 for 24-bit colour) corresponding to the pixels making up the image of a εelected region of the reεult of the agglutination aεεay. Each method iε therefore carried out three timeε : once on the image array (R(x,y), G(x,y) and B(x,y)) for each colour component of the image. In the final calculated value, the calculated values for each colour array are summed. If required, the contribution from any particular colour array may be reduced or omitted. The variable εize 1 repreεents the size (in units of length, such as millimeters) of one side of a square filter within which the pixel values are analysed. The variable εize2 represents the size (in units of length) of one εide of an additional εquare filter within which the pixel valueε may also be analysed. The variables a and b correspond to the lengths εizel and εize2 converted to numbers of pixels in the image. Thus, the square region defined by setting the value of sizel (size2) iε a square of a (b) pixels by a (b) pixels. According to each analyεiε method, one or more mathematical/statistical operations are carried out on the image array I(x,y) in each of the three colours (R,G,B) to generate a series of processed values. A histogram (frequency against procesεed value) of the processed values is generated and a lower percentage ("Low" in the Figureε) and a higher percentage ("High" in the Figureε) iε excluded from further calculation. Thuε, for example if Low=25% and High=25%, data from the firεt and fourth quartiles of the histogram iε excluded from further calculationε, and only data from the εecond and third quartiles is used. Thiε excluεion of data iε intended to reduce the effect of noiεe on the results. According to each method, the mean value of the proceεεed valueε (with the lower and higher percentages of data excluded) is calculated for each set of procesεed values generated from the red, green and blue arrays of image data. The calculated property value for the particular method is generated by summing the red, green and blue mean values, although one or more of theεe valueε may be excluded from the calculated property value, if deεired. Feaεibly, a weighted sum of the property values from each of the red, green and blue image array could be used to generate the final property value . Standard Deviation Method According to the εtandard deviation method, the εtandard deviation of each colour component (red, green and blue) within the filter window of the image array iε calculated. In the abεence of agglutination, the picture iε uniform with cloεe to zero deviation. In the presence of agglutination, the variation within a given area increases . According to this method, an area containing the agglutination pattern is selected and the pixels making up this region of the image are set as I(x,y) (in three colourε) . A filter window size, sizel, iε also selected and a corresponding pixel window size, a, iε calculated. The colour componentε (R, G or B) which are to be uεed to calculate the property value are alεo εelected, because depending on the colour of the agglutinateε it may be more effective to uεe only εome of the colour values . The standard deviation of the pixel valueε within a filter window (axa) centred on each current pixel (x,y) iε calculated and a εtandard deviation array Da(x,y) is thereby generated for each colour component of the image. For each colour component of the standard deviation array, a histogram of εtandard deviation valueε is generated and the Low percentage and the High percentage of data values are excluded from further calculation. The mean εtandard deviation value, mR,mG,mB, for each colour component iε then calculated from the remaining data. The calculated εtandard deviation value, p, is given as the sum of the mean standard deviation values, mR,mG,mB, for those colour components which were initially selected, i.e. according to the following algorithm: p = 0 if R selected then p = p + mR if G selected then p = p + mG if B selected then p = p + mB Fractal Signature Method According to the Fractal Signature method, two operators, MaxaO and MinaO, are used which respectively compute the maximum and minimum (R,G,B) pixel values (colour level valueε) inεide a window of εize a about the current pixel (x,y) . A combination of these operators can be used to generate an array containing only pixels which are part of a cluster of dimenεions less than a. The combination Maxa (MinaO) removes all peaks, i.e. regions of high localised pixel values, in the image of εize leεε than a, and the combination Mina(MaxaO) removeε all valleys, i.e. regions of low localised pixel values, in the image of size less than a. From an image array, I(x,y), a first structure array, Sa(x,y)= Mina (Maxa (I (x,y) ) ) - Maxa(Mina(I (x,y) ) ) , representing clusters in the image that are less than a in size can be generated. A processed image array, Fa(x,y)= Mina (Maxa (Maxa (Mina ( I (x,y) )))) , can also be generated to remove all the clusterε of εize less than a. Similarly, for a filter size b, which is larger than a, a second structure array, Sb (x,y) =Minb (Maxb (Fa (x,y) ) ) - Maxb (Minb (Fa(x,y) ) ) , can be generated representing cluεterε in the remaining image that are less than b in εize. The fractal signature, T(x,y) iε given by T(x,y) = log(Sa(x,y)/Sb(x,y) )/log(a/b) . Thuε, a value for agglutination can be generated in a correεponding manner to the standard deviation method, but in this case the fractal signature array, T(x,y) , iε used to generate the histogram, rather than the standard deviation array, Da(x,y). High Pass Method According to the High Pasε method, a mean operator, MeanaO, is used which computes the mean (R,G,B) pixel value inside a window of size a about the current pixel (x,y) . The high pasε array of pixel data is generated using two filter sizes, a and b, and is defined as Hab(x,y) = Abs (Meana (x,y) - Meanb (x,y) ) , where Abε repreεentε the abεolute value operator. The High Pasε array therefore repreεentε the degree of variation of the image array between the εcale of the smaller filter, a, and the scale of the larger filter, b. Thus, a value for agglutination can be generated in a corresponding manner to the εtandard deviation method, but in thiε caεe the high pass array, Hab(x,y), is used to generate the histogram, rather than the εtandard deviation array, Da(x,y). Colour Level Difference Method (CLDM) According to the Colour Level Difference Method of analyεis, the (R, G or B) colour value of the current pixel is compared to the (R, G or B) colour value of each pixel which is a diεtance a from the current pixel. Thuε, the CLDM value iε equal to Abε(I(x,y) - I(x',y')) for all pixelε (x',y') which are at a distance a from the current pixel (x,y) • Clearly, there are multiple CLDM values for each pixel as there are multiple neighbouring pixels and thus according to this method, a histogram of CLDM value (0 to 255, for 24 bit colour) is generated directly, without generating a procesεed value array. It will be seen therefore that the CLDM values provide an indication of the degree of colour variation in the image on the scale of the current filter size, a. The histogram iε normaliεed (each frequency value is divided by the total number of data items) and the Low and High percentages of data are discarded as with the preceding methodε . Thuε, for each colour component (R, G and B) , a respective normalised hiεtogram, h(i), iε generated with the variable i repreεenting the possible valueε of the colour level difference (0 to 255, for 24 bit colour) . For each colour component any of the following parameterε can be calculated by summing over all values of i: (a) CLDM-Mean: v = Σ ixh(i) (b) CLDM-Energy: v = Σ h(i)xh(i) (c) CLDM-Contrast: v = Σ i 2 xh(i) (d) CLDM-Homogeneity: v = Σ h(i)/(i+l) The calculated CLDM value, p, iε given aε the εum of the CLDM parameter, vR,vG,vB, for thoεe colour componentε which were initially selected for inclusion in the calculated value, i.e. according to the following algorithm: p = 0 if R selected then p = p + vR if G selected then p = p + vG if B selected then p = p + vB T-r-iTmngrl Mean Method According to the trimmed mean method, for each colour component (R, G, B) of the image array, a histogram of colour level value, i.e. pixel value, iε generated and the Low percentage and the High percentage of data valueε are excluded from further calculation. The mean colour level value, mR,mG,mB, for each colour component iε then calculated from the remaining data. The calculated trimmed mean value, p, is given as the sum of the mean valueε, mR,mG,mB, for those colour componentε which are εelected for incluεion in the reεult. Thus, in this case no mathematical/statiεtical operation iε carried out on the image arrayε before the hiεtogram is generated. Although the present invention has been deεcribed in termε of a diagnoεtic εyεtem and method of applicability to the field of medical testing, it will be appreciated that the invention is of applicability in any field where a quantified result is required by analyεiε of an agglutination aεsay. Furthermore, the invention has been deεcribed with particular reference to a personal computer. As will be understood from the foregoing, any general-purpoεe computer may be employed for the purpoεeε of the invention and this is intended to be encompasεed within the εcope of the appended claims.

Claims: Claimε 1. Apparatus for the analysis of an agglutination aεεay compriεing: an imaging device arranged to generate a digital image of an aεεay reεult compriεing a mixture of a εample and at least one agglutination reagent; and data procesεing means arranged to process said digital image to generate a quantitative result representative of the degree of agglutination of the sample and reagent. 2. Apparatuε aε claimed in claim 1, wherein the imaging device is a desk top, flat bed computer scanner. 3. Apparatus as claimed in claim 1 or 2, wherein the data proceεεing meanε comprises a personal computer. 4. Apparatus as claimed in any preceding claim, wherein the digital image is a digital colour image. 5. Apparatuε as claimed in any preceding claim, wherein the data procesεing meanε iε arranged to locate automatically digital image data corresponding to said assay result within the digital image. 6. Apparatus as claimed in any preceding claim, wherein the data processing means is arranged to determine at least one statiεtical characteriεtic of the distribution of pixelε within the digital image. 7. Apparatus as claimed in any preceding claim, wherein the data procesεing meanε iε arranged to determine the proportion of an area of the digital image representative of agglutination products. Apparatus as claimed in any preceding claim, wherein the data procesεing means is arranged to locate within the digital image clusters of contiguous pixels which are representative of agglutination products. 9. Apparatus as claimed in claim 8, wherein the data proceεεing meanε iε arranged to generate the quantitative reεult by reference to the area of the cluεterε. 10. Apparatus as claimed in claim 8 or 9, wherein the data procesεing meanε is arranged to generate the quantitative result by reference to the distribution of the clusterε in the digital image. 11. Apparatuε aε claimed in any of claims 8 to 10, wherein the data proceεεing meanε iε arranged to generate the quantitative reεult by reference to the number of the clusterε in the digital image . 12. A method for the analysis of an agglutination assay comprising the steps of: generating a digital image of an aεεay result compriεing a mixture of a εample and at leaεt one agglutination reagent; and processing εaid digital image to generate a quantitative reεult representative of the degree of agglutination of the sample and reagent . 13. A method for performing an agglutination assay comprising the steps of: providing a sample; providing at leaεt two agglutination reagents, each having different optical properties; mixing the sample and the reagents to form an assay result; generating a digital image of the assay result; and processing said digital image by reference to the optical properties of each reagent to generate a quantitative result representative of the degree of agglutination of the sample and each reagent. 14. A method as claimed in claim 13, wherein the optical properties are the colours of the reagents. 15. A method as claimed in any of claims 12 to 14, wherein the digital image is a digital colour image. 16. A method as claimed in any of claims 12 to 15, wherein the processing step compriεes automatically locating digital image data corresponding to the assay result within the digital image . 17. A method as claimed in any of claims 12 to 16, wherein the procesεing step compriεeε determining at leaεt one εtatiεtical characteriεtic of the diεtribution of pixelε within the digital image. 18. A method aε claimed in any of claimε 12 to 17, wherein the proceεεing step comprises determining the proportion of an area of the digital image representative of agglutination productε . 19. A method aε claimed in any of claimε 12 to 18, wherein the processing step compriεes locating within the digital image clusterε of contiguouε pixelε which are repreεentative of agglutination productε. 20. A method as claimed in claim 19, wherein the processing step comprises generating the quantitative result by reference to the area of the clusterε. 21. A method aε claimed in claim 19 or 20, wherein the proceεεing εtep comprises generating the quantitative result by reference to the distribution of the clusters in the digital image . 22. A method as claimed in any of claims 19 to 21, wherein the processing step comprises generating the quantitative result by reference to the number of the clusters in the digital image. 23. Computer software which when run on data processing means proceεεeε a digital image of an aεεay reεult compriεing a mixture of a εample and at leaεt one agglutination reagent, and generateε a quantitative reεult representative of the degree of agglutination of the εample and the reagent in accordance with the method of any of claimε 12 to 22.

Inventors: BREMNES DAG, GOGSTAD GEIR OLAV, SUNDREHAGEN ERLING, BREMNES, DAG, GOGSTAD, GEIR, OLAV, SUNDREHAGEN, ERLING
Applicants: AXIS BIOCHEMICALS ASA, BREMNES DAG, DIXON PHILIP MATTHEW, GOGSTAD GEIR OLAV, SUNDREHAGEN ERLING, BREMNES, DAG, DIXON, PHILIP, MATTHEW, GOGSTAD, GEIR, OLAV, SUNDREHAGEN, ERLING
Application year: 1999
Main classification: G01N21
IPC codes: G01N21, G01N33, G06T1, G06T7