Patent Publication Number: US-2009221011-A1

Title: Coagulation test system

Description:
FIELD OF THE INVENTION 
     The invention relates to a coagulation test system for measuring the coagulation of blood in a physiological sample fluid. 
     BACKGROUND OF THE INVENTION 
     The process of blood coagulation is complex and involves a large number of blood components including the generation of fibrin fibres. The fibres are formed by the polymerization of molecules of a protein called fibrinogen. Fibrinogen is catalyzed from an enzyme called thrombin, which is itself catalyzed from the enzyme prothrombin. 
     The prothrombin time test (PT test) is commonly employed in hospitals, clinics and laboratories to ascertain the ability of a blood sample to clot. The test is extensively used for pre-operative evaluations and for anti-coagulant therapy administered to cardiac patients, for example. The PT test is based upon the length of time required for a sample of blood to clot under the influence of certain reagents such as calcium ions and thromboplastin. 
     Similarly, individuals suffering from cardiac and vascular diseases and/or having mechanical heart valves are often treated with a daily regimen of blood thinning drugs commonly referred to as anticoagulants. The amount of anticoagulant in the blood stream, to be effective, must be maintained at a level deemed to be proper by a physician. The consequence of improper amounts of anticoagulant in the blood stream is serious, leading to strokes or haemorrhages. 
     Patients achieving this balance must endure frequent, costly and inconvenient visits to a clinic where the blood&#39;s ability to clot can be closely monitored. The monitoring is undertaken with periodic PT measurements as measured by the International Normalized Ratio (INR). For example, an INR greater than 3 results in a higher risk of serious haemorrhage, whilst an INR of 6 increases the risk of developing a serious bleed nearly 7 times that of someone with an INR below 3. In contrast, an INR below 2 is associated with an increased risk of stroke. Therefore, monitoring of the prothrombin time is recommended to ensure that the dose levels are within the therapeutic range. 
     By monitoring components such as fibrinogen and prothrombin levels within the blood, a physician may acquire meaningful data concerning a patient&#39;s blood clotting abilities or other clinical conditions. The proteins that are involved in the clotting (coagulation) process are commonly referred to as factors. The factors are numbered I-XIII, and reference to a factor by its number identifies the corresponding protein to those skilled in the art. 
     The activation of prothrombin occurs as a result of the action of blood clotting Factor Xa, which is formed by the activation of Factor X during proteolysis. There are two molecular pathways that lead to the activation of Factor X to give Xa, generally referred to as the extrinsic and intrinsic pathways for blood clotting. The extrinsic pathway utilizes only a tissue factor specific to an injured membrane while the intrinsic pathway utilizes only factors internal to the circulating blood. Both of these pathways originate with the interaction of enzymes involved in the blood clotting process with surface proteins and phospholipids. 
     Various tests have been introduced to measure the coagulation process in both the extrinsic and intrinsic pathways of a patient&#39;s blood sample. For example, the Activated Partial Thromboplastin Time (APTT) test measures the coagulation factors of the intrinsic pathway. These factors include Factors XII, XI, X, IX, VIII, V, II and I which may be abnormal due to heredity, illness, or the effects of heparin therapy. Thus, the APTT test is useful as a pre-surgical screen and for monitoring heparin therapy. Similarly, the testing of the fibrinogen polymerization rate using a Thrombin Time (TT) test or a quantitative fibrinogen test providing useful diagnostic data for patients on Warfarin therapy (brand name: Coumadine®) or related pharmaceuticals. 
     As mentioned previously, the test most commonly used to monitor anticoagulant therapy is the one-stage prothrombin time test. The reaction measured by the PT test is: 
       Blood+Thromboplastin+Ca ++ →Fibrin Clot 
     Thromboplastin is a phospholipid-protein preparation that activates clotting in blood specimens. Thromboplastins are commercially available from different manufacturers and can be obtained from lung, brain, or placenta extracts and also be synthetically manufactured. Generally, PT values between different laboratories are not in concordance, thus making such values unacceptable for defining therapeutic ranges for anticoagulant therapy. 
     An International Normalized Ratio (INR) was therefore developed and adopted by the World Heath Organisation in the early 1980&#39;s. The object of the normalised ratio was to standardise results from various thromboplastins and coagulation analyzers to become equivalent. Consequently, under the ratio a manufacturer assigns an International Sensitivity Index (ISI) to each batch of thromboplastin which indicates the relative sensitivity of the thromboplastin compared to an international reference thromboplastin. For example, if a thromboplastin has the same sensitivity as the reference thromboplastin, then the ISI is 1.0. An ISI value greater than 1.0 indicates that a thromboplastin is not as sensitive as the reference thromboplastin. The equation below is used to calculate the INR value using a PT value and a ISI value: 
     
       
         
           
             INR 
             = 
             
               
                 ( 
                 
                   
                     PT 
                     Patient 
                   
                   
                     PT 
                     
                       mean 
                       - 
                       normal 
                     
                   
                 
                 ) 
               
               ISI 
             
           
         
       
     
     The mean normal PT is determined in each laboratory by averaging the PT values from a number of healthy individuals. 
     The detection of the formation of fibrin clots date back to the mid 1850&#39;s and early methods were manual. By 1910, an apparatus to determine the change in viscosity of a blood sample as it underwent clotting was developed. The apparatus provided a direct indication of voltage which could be plotted against clotting time. In the 1920&#39;s, photoelectric techniques became prominent to detect variations in light transmittivity of a blood sample during clotting with variations in the optical transmittivity of the sample observed by a galvanometer. Further investigations of the coagulation of blood plasma using improved photoelectric techniques were conducted in the mid 1930&#39;s with optical density increasing as blood coagulated being observed. This led to the development of an instrument which displayed increasing density as a clot formed. 
     Modern optical density detection systems therefore operate on the principle that an increase in the optical density of a coagulating sample decreases the transmittivity of light through the sample. In a typical optical density detection system, a test blood sample is placed in a transparent sample cuvette and reacted with a coagulation stimulating reagent such as thromboplastin. Light or electro-magnetic radiation in the visible or near-infrared spectrum is then passed through the plasma-reagent mixture as the sample clots. As the biochemical change leading to fibrin formation takes place within the sample, the optical density of the sample increases. Output voltages corresponding to the optical density of the sample enables, after processing with a processing unit, to determine the coagulation of the sample. 
     While the existence of the relationship between fibrinogen (fibrin) levels and optical density has long been recognized, there has been wide disagreement concerning the nature and proper methodology for measuring the relationship, and numerous test parameters have been devised for determining fibrinogen levels using optical density data. 
     Further, the increased awareness about the negative effect of irregular blood coagulation time, the acceptance of self-monitoring and self-treatment has led to the development of a multitude of blood coagulation monitors and methods for personal use and point of care testing. However, these devices still lack the development state, economy, and convenience known form home glucose monitoring systems for diabetes patients. 
     An exemplary method and system for measuring blood coagulation time is disclosed in U.S. Pat. No. 4,252,536. The method involves providing a mixture of a blood sample and a reagent, irradiating the mixture with light and detecting the amount of light scattered from the irradiated mixture producing an electrical signal representative thereof. Subsequently, a determination is made from the electrical signal a time at which the most rapid change in electrical signal is occurring and then determining as the end point at a time prior to the first time at which a change which 1/n that of the most rapid change occurred, where n is greater than 1. Most of the methods of measuring coagulation time are based on plasma being introduced into a cuvette and to analyse the properties of coagulation over a period of time. 
     European Patent Application 1,162,457 discloses a testing system for determining an appropriate coagulation promoting substance for administration to a patient as a therapy for improving clotting function using three sample wells to receive a selected amount of blood. 
     U.S. Pat. No. 6,066,504 discloses an electrode assembly which provides quantitative measurement of viscosity changes over intervals of time to signal the coagulation or lysis of a blood sample. 
     European Patent 974,840 discloses fluidic diagnostic device for measuring an analyte concentration or property of a biological fluid using optical detection means. 
     PCT WO20047/044560 discloses a photometric determination of coagulation time in undiluted whole blood having a container for receiving a sample of undiluted whole blood, a light emission source for emitting light and a light detector for measuring an amount of light from said container. 
     U.S. Pat. No. 6,084,660 discloses a fluidic medical diagnostic device having at one end a sample port for introducing a sample and at the other end a bladder for drawing the sample to a measurement area, which measures an analyte concentration or a physical property of whole blood, particularly the coagulation time, only after first ensuring that a whole blood sample has been introduced into the device. 
     PCT WO2002/086472 discloses the use of fluorescent molecular rotors which vary in fluorescence intensity based on viscosity of the environment. The inventor further relates to a class of molecular motors that at modified with a hydrocarbon chain or hydrophilic group to allow for the measurement of membrane or liquid viscosity. 
     US Patent Application Publications US 2002/0110486A1 and US 2003/0031594 A1 disclose a test strip comprising a plurality of reaction zones utilised for quality assurance purposes. The test strip requires a volume of about 20 μL blood. However, if a user has to test frequently, as required for proper management of coagulation therapy, these large sample volumes are unpractical and disadvantageous. 
     PCT/EP 2004002284 discloses a dry reagent test element for the photometric detection and quantitative determination of an analyte, e. g. glucose, in a physiological fluid, e. g. blood, having a sample distribution system with at least two detection areas which is provided with an integrated calibration system and which requires very small sample volumes of about 0.5 μL. 
     However, up to now no test system exists, which is suitable for measurement of coagulation of a blood sample and which is provided with integrated quality control means and requires only small sample volumes. 
     Therefore, it is the object of the present invention to provide a test system for determining the coagulation of whole blood which requires only minimal steps, such as the application of blood onto a strip, which provides a subsequent automatic calculation of an accurate test result including a means for ‘on-strip’ quality control and which requires only a small sample amount. 
     It is a further object of the present invention, to provide a production process for a coagulation test element which does not involve many and complicated production steps and therefore is inexpensive and usable for products assisting patients in self-monitoring blood coagulation and/or in a physician&#39;s place of work. 
     SUMMARY OF THE INVENTION 
     Thus, the present invention provides a test element for the determination of coagulation in a plasma or whole blood sample having a first surface and a second surface in a predetermined distance opposite from each other, said both surfaces being provided with two substantially equivalent patterns forming areas of high and low surface energy which are aligned mostly congruent, whereby the areas of high surface energy create a sample distribution system with at least one detection area, wherein the detection area(s) of the first and/or second surfaces is/are provided with at least one coagulation stimulation reagent. 
     In another aspect the present invention provides a method for preparing a coagulation test element. 
     In a further aspect the present invention provides a coagulation test system consisting of a coagulation test element and a meter device for performing blood coagulation assays using a simplified format to provide a verified result in accordance with worldwide standards by providing on strip quality control. 
     A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of illustrative and preferred embodiments in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of one embodiment of the coagulation test element of the present invention provided in shape of a test strip. 
         FIG. 2  shows a perspective view of the embodiment according to  FIG. 1 , showing the sample distribution enlarged. 
         FIG. 3  shows an exploded perspective view of the device according to  FIG. 1 , showing the three layers separately. 
         FIG. 4  shows different forms of the discontinuity of the centre layer forming the sample cavity together with the first and second surface. 
         FIG. 5   a  is a sectional view of a detection area of the sample distribution system constructed by hydrophobic guiding elements. 
         FIG. 5   b  is a sectional view of another embodiment of a detection area of the sample distribution system using hydrophilic pathways. 
         FIG. 6  shows different embodiments of the sample distribution system with different patterns of pathways and detection areas suitable for different evaluation methods. 
         FIG. 7   a  shows the sample distribution system of  FIG. 5   b  in conjunction with a light emitter and detector arrangement in a section view suitable to evaluate the changes in light absorbance of the sample. 
         FIG. 7   b  shows the sample distribution system of  FIG. 5   b  in conjunction with a detector means configured to evaluate the changes in the fluorescence signal of a molecular rotor added to the sample or to evaluate the turbidity of the supplied sample fluid. 
         FIG. 8  shows different molecular rotors and their molecular structure; 
         FIG. 9  is a graph showing the schematic evaluation of coagulation results with implemented positive and negative quality controls. 
         FIG. 10  shows the optical spectrum of whole blood from 500 to 700 nm. 
         FIG. 11  provides a graph displaying the progress of a blood coagulation reaction initiated with Thromborel S® and monitored at 600 nm. 
         FIG. 12  shows a simplified block diagram of an example meter for use in a method of the invention. 
         FIG. 13  shows the influence of registration failures during the lamination process on the sample volume of the test element and the top respectively the sectional view of an alternative embodiment, which allows higher tolerances for the registration of base and cover layer without compromising on the test strip quality. 
         FIG. 14  shows the production steps of the coagulation test elements with strip shape. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1  and  FIG. 2 , the coagulation test strip  1  of the present invention is a multiple layer arrangement comprising a base layer  2 , a centre layer  3  overlaying the base layer  2 , and a cover layer  4  overlaying the centre layer  3 . The centre layer  3  presents a discontinuity  5 , which creates a hollow cavity in conjunction with the base layer  2  and the cover layer  4 . Within said cavity there is located a sample distribution system  6  which is connected to a sample application area  9  located on one side of the coagulation test strip. The sample application area  9  as interface to the user is preferably formed by a convex curve  10  extending from one major side of the coagulation test strip for easier application of the sample. Opposite to the sample application area  9 ,  10  on the second major side of the coagulation test strip is the location of an air vent  11  allowing the displacement of air while the physiological or aqueous fluid is distributed to the predetermined detection areas  6   a ,  6 ′ a  (see  FIG. 3 ). It might be noted that the construction requires only one air vent independent of the amount of predetermined detection areas used within the coagulation test element. The described elements of the sample distribution system with areas of high surface energy, sample application area, air vent, centre layer and discontinuity in the centre layer form the totality of the coagulation test element, which creates the intrinsic capillary action to exert the distribution of the applied physiological or aqueous fluid to the predetermined detection areas. 
     In addition, the coagulation test strip  1  possesses registration features  7 ,  8  useful to differentiate between several kinds of test strips for the determination of different parameters such as Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT). By this means, a multi analyte meter could be instructed to run a special program or procedures with selectable parameters upon strip insertion required for the determination of different parameters. As illustrated in  FIG. 3 , which represents the multi-layer arrangement of  FIGS. 1 and 2  in an exploded view, the base layer  2  provides a first surface  2   a , and the cover layer  4  provides a second surface  4   a . The first surface  2   a  and the second surface  4   a  are patterned with areas which will create the sample distribution system  6 . The pattern of the sample distribution system  6  comprises a predetermined number of detection areas  6   a  and sample pathways  6   b , which are aligned and registered mostly congruent upon assembly of the multi-layer arrangement. The centre layer  3  defines the distance between the first surface  2   a  of the base layer  2  and the second surface  4   a  of the cover layer  4  and has a discontinuity  5  to form a hollow cavity together with the first surface  2   a  of the base layer  2  and the second surface  4   a  of the cover layer  4 . The sample distribution system  6  which will be formed between the first surface  2   a  and second surface  4   a  is located within the cavity created by the discontinuity  5  of the centre layer  3  and the first surface  2   a  of the base layer  2  and the second surface  4   a  of the cover layer  4 . Preferably, the hollow cavity is substantially larger by design than the sample distribution system. 
     Since the purpose of the discontinuity  5  of the centre layer is only to create a cavity for the sample distribution system  6 , the discontinuity  5  of the centre layer  3  can have different forms; examples thereof are shown in  FIG. 4 .  FIG. 4   a  shows an umbrella shaped coagulation test element cavity  12 .  FIG. 4   b  shows a rectangular coagulation test element cavity  13 , and in  FIG. 4   c  the sample cavity  14  has a circular shape. The discontinuity  5  of the centre layer  3  does not influence the size of the predetermined detection areas  6   a  and the size of the pathways  6   b  of the sample distribution system  6  and therefore does not influence or change the required sample volume. Compared to the sample distribution system  6 , the cavity shapes shown in  FIG. 4  are rather simple, thus allowing the application of simple punch tools and fast processing with less demand on the registration accuracy. 
     The sample distribution system  6  located in the cavity formed by the discontinuity  5  of the centre layer  3  and the first surface  2   a  of the base layer  2  and the second surface  4   a  of the cover layer  4  is formed by creating areas of high and low surface energy on said surfaces  2   a  and  4   a . The areas of high and low surface energy on the first surface  2   a  of the base layer  2  and the second surface  4   a  of the cover layer  4  are aligned and registered mostly congruent to each other. Since the applied physiological fluid or any other aqueous sample is wetting only the areas with high surface energy, it is thus constrained within the predetermined flow paths  6   b  and detection areas  6   a  of the sample distribution system  6  and between the first surface  2   a  of the base layer  2  and the second surface  4   a  of the cover layer  4 . 
       FIG. 5   a  shows a construction of the sample distribution system  6  using hydrophobic “guiding elements”. In this embodiment of the coagulation test element of the present invention the base layer  2  and the cover layer  4  are coated with a hydrophobic layer  16 , except the areas, which will form the sample pathways and detection areas. The hydrophobic layer  16  creates an area with low surface energy, which will exert a repellent force onto an applied sample fluid  15  and constrain the sample fluid  15  therefore to the areas of high surface energy which will form the sample distribution system  6 . 
     Preferably, the hydrophobic layer is applied on a hydrophilic surface, which is wet-table by the physiological or aqueous fluid. The procedure described above requires a hydrophilic surface, which can be produced from a natural hydrophilic polymer such as cellophane or glass as well as from a hydrophobic surfaces of common polymers (examples are given below) by rendering the hydrophobic surface hydrophilic using a coating process or physical or chemical plasma deposition of hydrophilic monomers that can be vaporised in vacuum, e. g. silicon dioxide, ethylene oxide, ethylene glycol, pyrrole or acrylic acid. Subsequently, the pattern of “guiding elements” can be realized by printing hydrophobic ink on the hydrophilic surfaces of the base and cover layers. 
     A suitable hydrophobic ink will have contact angles with water of typically more than 100° and a surface energy of typically less than 25 mN/m and contain typically monomers, oligomers, and polymers with hydrophobic functions, hydrophobing additives, or hydrophobic pigments and fillers. 
       FIG. 5   b  shows another construction of the sample distribution system using hydrophilic pathways. In this embodiment of the coagulation test element the base layer  2  and the cover layer  4  are coated with a hydrophilic layer  17  thereby creating areas of high surface energy. 
     The hydrophilic layer  17  printed on the hydrophobic surface is highly wettable by a physiological or aqueous fluid; thus, the areas of high surface energy creating the hydrophilic pathways of the sample distribution system will exert a positive capillary force onto the applied physiological or aqueous sample fluid to transport the sample fluid to the separate detection areas. 
     The hydrophilic layer  17  can be realized by printing hydrophilic or amphiphilic agents on a hydrophobic surface. Inks with hydrophilic functions can be realised from a wide selection of high molecular weight water and alcohol soluble polymers and mixtures thereof. Particularly useful are derivatives prepared form alginates, cellulose, hydroxyethyl cellulose, gums, polyalcohols, polyethylene-glycols, polyethylene-oxides, vinylpyrolidone, polystyrene sulfonates, polysulfonates, alkyl-phosphocholine derivates and others; particularly useful are also organo-modified silicone acrylates, which are a cross-linkable species of organo-modified polysiloxanes and fluorinated surfactants. Suitable coatings provide a contact angle with water of typically less than 35° and a surface energy of typically more than 50 mN/m. 
     The base layer and cover layer suitable as substrate for the printing process may be formed of a material like glass, polyvinyl acetate, poly-methyl-methacrylate, poly-dimethyl-siloxane, polyesters and polyester resins containing fluorene rings, polystyrenes, polycarbonates and polycarbonate-polystyrene graft copolymers, terminal modified polycarbonates, polyolefins, cycloolefins and cycloolefin copolymers, and/or olefin-maleimide copolymers. 
     In case the substrate has an intermediate hydrophobic character, the printing of hydrophilic pathways with a surrounding hydrophobic pattern, i.e., a combination of the constructions of  FIG. 5   a  and  FIG. 5   b , is possible as well. 
     In an alternative embodiment (not shown), either the first or second surface is provided with the hydrophilic/hydrophobic pattern whereas the corresponding surface provides a homogeneous pattern of hydrophilic pixels surrounded by a hydrophobic area thereby creating a surface with semi hydrophilic and semi hydrophobic character (amphiphilic character), which eliminates the necessity to align the hydrophilic and hydrophobic pattern of the first surface with an equivalent hydrophilic and hydrophobic pattern of the second surface. The properties of such an amphiphilic surface can be easily designed by the geometric pattern of the hydrophilic pixels and the overall ratio between the hydrophilic and the hydrophobic area. In the disclosed invention the amphiphilic character, respectively the ratio between hydrophilic pixels and hydrophobic areas, is designed that the sample fluid progresses from hydrophilic pixel to hydrophilic pixel only if the opposite surface provides hydrophilic character. If the opposite surface provides hydrophobic character the movement of the fluid within the capillary gap of the coagulation test element will stop. This mechanism allows the above-described method to form a functional coagulation test element without the stringent requirement of precise registration of the corresponding pattern of the sample distribution system provided on the first and second surface. However, preferably both the first and the second surface are provided with equivalent patterns of high and low surface energy to ensure a quick distribution of the sample fluid within the hydrophilic pathways of the sample distribution system. 
     Moreover, it is possible to physically elevate the areas of high surface energy of first and second surfaces from the areas of low surface energy by etching, embossing, or simply by printing the hydrophilic layer with about three to five times increased thickness on the first and the second surface. Due to this elevation the capillary gap of the hydrophilic pathways gets smaller in relation to the surrounding area and exerts a higher capillary forth on the sample liquid. 
     The volume requirement for the sample distribution system contained in the coagulation test element of the preferred embodiment is with about 0.5 μL-1.0 μL very low and requires only about 100 nL-150 nL per detection area, whether the areas of high and low surface energy are created by hydrophobic guiding elements or hydrophilic pathways or by a combination of both. However, it will be obvious for the one skilled in the art that the volume of the sample distribution system will vary with various designs and with the number of employed predetermined detection areas. 
       FIG. 6  shows different patterns of the sample distribution system, which can be realized by hydrophilic pathways as illustrated in  FIG. 5   b , or by the hydrophobic “guiding elements” as illustrated in  FIG. 5   a , or by a combination of hydrophilic pathways and hydrophobic guiding elements. The selected sample distribution system needs to be appropriate for the selected physiological parameter to be evaluated and for the employed detection chemistry. 
     Thus, the repetition of sample and standard measurements is possible for particular serum or whole blood samples with the embodiments shown in row II to IV. Likewise, it is possible to use the coagulation test element provided in row IV for the evaluation of two coagulation parameters such as Prothrombin Time and Activated Partial Thrombin Time. 
     As stated above, the formation of a fibrin clot is dependent on a reaction between Thromboplastin and Calcium ions reacting with blood as shown below: 
       Thromboplastin+Ca ++ +Blood (or Plasma)→Fibrin clot  (Reaction 1) 
     For Reaction (1) to take place, the detection areas  6 ′ a  of the sample distribution system  6  of the first surface  2   a  of the base layer  2  or the second surface  4   a  of the cover layer  4  are characterised in that they are coated with formulations  18 ,  19 , as shown in  FIG. 5   a  and  5   b , which allow the promotion and detection of a coagulation reaction in a blood sample. 
     In one embodiment of the inventive test element, the formulation  18  contains a coagulation stimulating reagent, such as thromboplastin (e.g. available from Dade Behring Holding GmbH, Höchster Strasse 70, 65835 Liederbach, Germany), whereas formulation  19  contains calcium ions. The coagulation stimulating reagent is a promoter for the coagulation of blood in a detection area thus allowing the detection of the optical properties by transmission or absorbance photometry or light scattering. 
     The Prothrombin Time or the Activated Partial Thrombin Time can be monitored by change of light absorbance or light scattering. During the coagulation process the Fibrinogen is converted to Fibrin that forces the previously arbitrary distribution of the red blood cells and platelets into a mostly associated stage, whereby the red blood cells and platelets becoming trapped and connected with the Fibrin fibres and each other while forming the blood clot. These changes in the physical consistency of the blood sample leads to a reduction of scatter centres and therefore to a change in the light absorbance and turbidity of the examined blood sample. For the evaluation of the changes in light absorbance the detector arrangement shown in  FIG. 7   a  is suitable 
       FIG. 7   a  shows a detector arrangement for measuring the optical density of the sample within the coagulation test element according to  FIG. 5   b . The arrangement includes a light source  20 , which emits light  24  of a certain wavelength in direction of the sample detection area. The light emitted from the light source  20  passes through an optical arrangement  21 , e.g. a diffuser or lens, and an aperture  22 , the base layer  2 , the sample  15 , and the cover layer  4  of the detection area and is detected on the opposite side of the device by a detector means  23 . 
     In an other embodiment, the coagulation test element is designed to perform more than one determination to provide additional quality control measurements. In this case, the coagulation test element provides at least two, preferably three coagulation detection areas. Preferably, all of the detection areas  6 ′ a  on the first surface  2   a  are coated with the coagulation stimulating reagent  18  (e. g. Thrombin) promoting the reaction between the chemical components to generate a fibrin clot, whereas one sample detection area, e. g.  6   a   2 , of the second surface  4   a  is coated with a chemical formulation containing a coagulation accelerator promoting a fast and complete coagulation (positive control), and an other detection area, e. g.  6   a   3 , of the second surface  4   a  is provided with a chemical formulation containing a coagulation inhibitor suppressing the coagulation of blood (negative control). 
     For Reaction (1) to take place, the quantities of thromboplastin, calcium ions and, if necessary, quality control formulations, such as a coagulation inhibitor or accelerator, are precisely dosed on said sample detection areas. Preferably, the dosing is performed by drop on demand deposition methods, although other techniques such as ink jet printing would be known to persons skilled in the art. The exact dosing of the coagulation stimulating reagent applied to the sample detection areas is critical for a proper reaction procedure and thus for a reliable calculation of the end point of a coagulation reaction. For instance, in an example embodiment, the amount of thromboplastin can be constant throughout each sample detection area, whilst the concentration of coagulation inhibitor, such as EDTA, can be varied. 
     In a further embodiment of the inventive test element, in addition to the dosing of thromboplastin, calcium ions and quality control formulations, such as a coagulation inhibitor and accelerator, a further component, which functions as a fluorescence detection aid, can be applied to the sample detection areas of the first and/or second surface(s)  2   a ,  4   a . If said detection areas are supplied with so called fluorescent molecular rotors, the coagulation reaction can be monitored by fluorescence. 
     Fluorescence is the emission of light from any substance and occurs from the first excited state of a molecule. In the initializing process such a molecule is excited by absorption of light. In the course of the following few nanoseconds the molecule returns to its ground state and gets rid of its excitation energy either by emission of light—called fluorescence—or by movements and rotations of its molecular backbone. 
     Fluorescence typically occurs from aromatic molecules. Aromatic molecules absorbing visible light in the range between 400 and 800 nm appear coloured. Furthermore, a chromophore is the part of a dye that determines the absorption and emission properties of the whole molecule. The amount or intensity of emission of a specific chromophore is quantified by its fluorescence quantum yield. The fluorescence quantum yield is defined as the number of emitted photons relative to the number of absorbed photons. A wide range of commonly used fluorescence dyes have a fixed quantum yield, whereby all dyes with large quantum yields approaching 100% emission efficiency displays the brightest emissions, such as Sulforhodamine 101 also known as Texas Red. 
     Dyes carrying flexible groups at the end of their chromophore are known as molecular rotors and show a dependence of their fluorescence quantum yield on the viscosity of the solvent. As the viscosity of the solvent increases, the fluorescence quantum yield of those dyes increases. This effect can be attributed to the mobility of the flexible, non-rigid groups at the end of the chromophore which is lowered by increasing viscosity. The more mobility of the side groups attached to the chromophore is hindered, the more the dye molecule cannot relax to its ground state via movements of its molecular scaffold and gets rid of its excitation energy by emission of light. Examples for fluorescent dyes sensitive to the viscosity of the solvent can be found in the classes of xanthene, oxazine and carbopyronine dyes. 
     The effect can be attributed to the mobility of the diethylamino groups which is lowered by increasing viscosity. One example of such a dye in the xanthene class is Rhodamine B which is shown as a chemical structure below: 
     
       
         
         
             
             
         
       
     
     The chemical structure below shows as way of example the mobility of the diethylamino groups which is subsequently lowered by contact to the reagents of reaction 1. Since the reagents lead to the formation of a fibrin clot, i.e. the coagulation of a physiological fluid, the viscosity of the sample increases and subsequently the fluorescence of the molecules. The marked diethylamino-groups at the end of the chromophore are non-rigid and rotate as marked around the bond. As this movement is strongly hindered by increased viscosity because of coagulation, the fluorescence emission of the dye is increased. 
     
       
         
         
             
             
         
       
     
     In respect to the disclosed invention fluorescence probes sensitive to change in the viscosity are most useful. Further examples of molecular rotors are Auramine O., Crystal violet 4, p-N,N-dimethylaminobenzonitrile 5, p-N,N-dimethylaminobenzonitrile 6, Julolidinebenzylidenemalononitrile, Rhodamine 19, Rhodamine G6, Rhodamine B, Oxazine 1, Oxazine 4, Oxazine 170. Their molecular structures are shown in  FIG. 8 . 
     In case the reaction is monitored by fluorescence it is most useful to arrange the light source and the detection means not opposite each other and rather in an angle of approximately 90 degrees to achieve maximum sensitivity, as shown in  FIG. 7   b . The preferred angle between the light source and the detection means is between 80 and 120 degrees but most preferably it is approximately 109 degrees and the coagulation test system is placed in the optical detection arrangement in way that the angle between the base layer and the light source and the angle between the cover layer and detection means is approximately 54 degrees to avoid background noise due to internal reflections on the different surfaces of the detection area (or more generally of the coagulation test system). For full operation said detector  23  is configured in addition to the optical arrangement  21  and  22  with the optical filters  21   a  and  22   a  to discriminate between the excitation and the emission wave length, thus the detection means will only see the light  24  emanating from the fluorescence dyes and not the light  24   a  originated by the light source. Albeit, one skilled in the art will notice that the actual angle has to be optimised for a specific application, the required sensitivity, and the requirements of the meter respectively the detection device. 
     The coagulation test element  1  has at least one detection area  6   a  which is required for an accurate prothrombin time measurement, but in a preferred embodiment three detection areas  6   a   1 - 6   a   3  can be utilised. The physical make up of coagulation test element  1  allows flexibility in the composition of compounds applied in various detection areas. For instance, detection areas  6   a - 6   c  can have different concentrations of the coagulation stimulating reagent, such as thromboplastin, applied on a first surface  2   a  of a base layer  2  whilst calcium ions and the fluorescent molecular rotor can be applied to a second surface  4   a  of a cover layer  4 . Alternatively, all reagents can be applied either on the first surface  2   a  of the base layer  2  or the second surface  4   a  of the cover layer  4  of the coagulation test element  1 . 
     After the physiological fluid, such as blood or plasma, is applied to the sample application area  9  and distributed to the detection areas by capillary action, it dissolves the coagulation stimulating reagent contained in the formulation  18  on the detection areas of the first surface  2   a  as well as the molecular rotor and/or a potential coagulation inhibitor such as EDTA contained in the formulation  19  on the predetermined detection areas of the second surface  4   a  forming a mixture of blood or plasma and coagulation stimulating reagent such as thromboplastin, and calcium ions plus the additional materials provided on the second surface. 
     Preferably, the coagulation stimulating reagents applied to the predetermined detection areas are readily soluble by a physiological fluid such as blood and positioned close to each other to allow rapid diffusive mixing of all components, thus enabling a fast reaction of the components contained in the detection areas to expedite a fast photometric determination of the forming coagulation reaction. 
     If there are more than two, preferably three, sample detection areas arranged within the sample distribution system, one, e.g.  6   a   1 , can be used to detect the Prothrombin Time or the Activated Partial Thromboplastin Time. An additionally sample detection area, e.g.  6   a   2 , can be configured to provide a negative control using a coagulation inhibitor on the second surface  4   a  or omitting the coagulation stimulating agent on the first surface  2   a , whereby a further sample detection area, e.g.  6   a   3 , can be configured to provide a positive control using a coagulation accelerator, e.g. a gelling agent mimicking the coagulation of blood even if blood would posses a coagulation deficiency. Thus, the processing means of the measurement device can compare the measurement result of the sample with the two provided standards allowing a clear decision or the indication of an erroneous measurement. 
       FIG. 9  shows a schematic evaluation and measurement of the coagulation time using a molecular rotor as fluorescence probe and detection aid. The figure also shows the comparison of the measurement signal related to a blood sample  27  with a positive standard  26  providing the maximum fluorescence achievable after the full formation of the blood clot and the comparison with a negative standard  25  providing minimum fluorescence signal related to a non coagulated blood sample. After the application of the whole blood sample onto the sample application area  9  the blood sample  15  is transported by capillary action created by the sample distribution system to the different sample detection areas  6   a / 6 ′ a  shown in  FIG. 3 . The sample will dissolve the coagulation stimulating reagent provided on the first surface  2   a  of the base layer  2  allowing the coagulation reaction to start immediately after the sample detection area  6 ′ a   1  is filled. The detection unit of the measurement device will register the introduction of the blood sample thus the processing means of the detection device can initiate to allow a time resolved evaluation of the coagulation reaction. 
     As mentioned above, one sample detection area, e. g.  6   a   2 , can be configured as negative standard providing the means of comparing the measurement signal of the blood sample in sample detection area  6   a   1  with the measurement signal of a blood sample showing no coagulation reaction. Such behaviour can be achieved either by the deposition of non coagulation stimulating reagent in sample detection area  6 ′ a   2  or by the deposition of an coagulation inhibitor on sample detection area  6   a   2 . Typical coagulation inhibitors are lithium heparin and sodium respectively the potassium salt of ethylenediaminetetraacetic acid (EDTA). 
     On the other hand, a positive standard can be realised by accelerating the coagulation reaction or by mimicking the viscosity of a fully formed blood clot with a different cross-linking agent, which provides a faster reaction time than a non pathogen blood sample, thus the positive reference value is achievable before the blood sample in detection area  6   a   1  is coagulated. This kind of cross-linking can be achieved providing the right concentration of alginate on the second surface  4   a  of the second layer  4 . The alginate will mix with the blood and begin to gel respectively coagulated due to the reaction with the calcium ions inside the blood sample and/or additional calcium ions provided on the first surface of the base layer. However, one skilled in the art will recognize that other gelling agents might be applicable and useful for this reaction as well. 
     During the reactions the processing means of the measurement device can compare the reading of sample detection area  6   a   1  with the negative standard  25  and the positive standard  26 . As soon as measurement signal of the blood sample, provided by sample detection area  6   a   1 , reaches the same magnitude as the positive standard (indicated with numeral  28  of  FIG. 9 ) a processing unit of the measurement device can stop the timer and evaluate the final result. Further the processing unit can perform some additional quality checks to verify that the analysis was performed correctly and provides meaningful data to the user/patient. In this respect, the processing unit can compare the actual measurement values of the positive and negative standards, which needs to be separated by a minimum and pre-programmed value. If the amplitude of both signals becoming to small the device can issue an error message that the determination was not successful. Further the device can calculate the slope  27  of the coagulation reaction and compare it again with some pre-programmed physiological values which describe the most extreme values observed by clinicians. 
     While monitoring the turbidity of the sample over a wide range of the spectrum, e. g. by using a halogen lamp as light source, it is useful to restrict the monitoring window to a narrow part of the spectrum if the sample changes are monitored by light absorbance.  FIG. 10  shows a spectrum of whole blood between 500 and 700 nm. The prevalent feature of the spectrum is the haemoglobin double peak  40  between 520 and 600 nm. Principally, one can evaluate the progress of the coagulation reaction by light absorption anywhere in the provided region of the whole blood spectrum it is less demanding on the technical measurement device if the reaction is monitored at a wave length outside of the haemoglobin absorbance range i.e. 600 nm as indicated by numeral  41 . 
       FIG. 11  provides an exemplary evaluation of coagulation reaction by light absorption at 600 nm. Blood is introduced in the coagulation test element via the sample application port  9  and the transmission of light is rapidly reduced respectively the absorbance of light is rapidly increased as indicated by numeral  42 . Subsequently the coagulation formulation provided in the sample detection areas  6 ′ a  of the first surface  2   a  of the base layer  2  is dissolved and the coagulation reaction is initiated by the reaction of the tissue factor (tissue thromboplastin) with the blood or plasma sample. This point in time is defined as t=0 and the processing unit will start the recording of measurement data. The period of time between the events  42  and  43  can be understood as the lag phase of the reaction, here the full dissolution of the reagents and mixing with the blood or plasma sample is achieved and the tissue thromboplastin triggers a series of coagulation factors of the extrinsic pathway. Showing in the sequence the activation of factor VII, factor X, factor V, factor II. The last stages of the coagulation cascade can be monitored between event  43  and  44  where the fibrinogen is transformed into fibrin. Often the fibrin clot is not stable and starts deteriorating after the plateau  44  is reached. The deterioration rate and quantity depend on the amount of fibrin fibres in clot and varies form patient to patient. Normally, highly viscose blood samples show a slower deterioration then low viscose blood samples. 
     The result of the measurement generally and the result of the Prothrombin Time according to the above example have to be evaluated between the events  42 - 43  indicating the time period t 1 , and between the events  43 - 44  indicating the time period t 2  following the generally equation 1: 
       PT= f   PT ( a·[f ( t   1 )]+ b·[f ( t   2 )])  Equation 1 
     The factors a and b are required to give a proportional weight to the time periods t 1 , and t 2 , which always contribute to different proportions to the result PT given by f PT . Whereby t 1  is influenced more by the type of the inert ingredients of the coagulation formulation that govern the dissolution of the tissue factor, t 2  is mostly influenced by the activity of the applied tissue factor itself and the calcium ion concentration. Additionally, both time period t 1  and t 2  are modulated by the reaction temperature, which should be ideally set to or close to 37° C., lower temperature regimes will prolong the coagulation time. However, for hand held devices one will always have to find the best solution between portability, energy consumption and laboratory performance. 
       FIG. 12  shows a simplified block diagram of a meter  80  for use in conjunction with the present invention. The meter  80  can be designed around a processing unit such as the MAXQ2000 microcontroller (available from Dallas Semiconductor Corporation, 4401 South Beltwood Parkway, Dallas, Tex., USA). The processing unit  81  can serve the following control functions: (1) timing for the entire system; (2) processing the data from the light detection means; (3) calculating PT time from the measured data; and (4) outputting PT time or INR value to a display means  83 . A memory circuit can store data and the processing unit operating program. The display means  83  can take various forms such as liquid crystal or LED display. The meter  80  can also include a start-stop switch and can provide an audible or visible time output to indicate for applying samples, taking readings etc., if desired. 
     Processing unit  81  may be programmed with software to allow it to make, in conjunction with meter  80  a coagulation measurement. The light emitted from the light source  20  passes through an optical arrangement  21 , and detected by a detection means  23 . The software programmed into processing unit  81  can further contain an algorithm to calculate the coagulation time as an International Normalised Ratio, formulated in the mid-1980&#39;s, to standardise PT values so that results from different thromboplastins and coagulation analysers become equivalent. The expression is given below as: 
     
       
         
           
             
               
                 
                   INR 
                   = 
                   
                     
                       ( 
                       
                         
                           PT 
                           Patient 
                         
                         
                           PT 
                           
                             mean 
                             - 
                             normal 
                           
                         
                       
                       ) 
                     
                     ISI 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
     where ISI is the International Sensitivity Index, PT patient is the time for coagulation for a blood sample from a patient, mean normal PT is the average PT time for around 20 individuals. The ISI value is given by the different manufactures of Thromboplastin. 
     The method of using coagulation test element  1  of the present invention can be understood with reference to the block diagram of a meter shown in  FIG. 12 . The user inserts a coagulation test element  1  into a strip holder  82  of a meter  80  which is automatically activated by triggering a ‘push to make’ switch which may be integrated thereon. Registration features designed on element  1  engage with registration features on strip holder  82  to ensure that element  1  is placed in a correct position. Such correct placement of element is of paramount importance to ensure the operation of combined meter  80  and strip  1 . Optionally, the meter  80  can be activated by a user pressing a switch. Accordingly, a user performs a finger prick and applies whole blood to application area  9  of inserted coagulation test element  1 . 
     The volume of blood required for a test to take place in the present invention is in the order of 1 μL. Since the hydrophilic agent printed on the hydrophobic surface is highly wettable by a physiological or aqueous fluid, the areas of high surface energy creating the hydrophilic pathways of the sample distribution system will exert a positive capillary force onto the applied physiological sample fluid to transport the sample fluid to the separate detection areas. Therefore the physiological sample will rapidly distribute to each sample detection area ( 6   a - c ) and activate the coagulation stimulating reagents therein. 
     Next, coagulation test time starts since the reagent in detection areas  6   a - 6   c  aids in the coagulation process allowing the coagulation to take place and the optical properties are processed to give the point at which coagulation has occurred. 
     Preparation Method of the Coagulation Test Element 
     The coagulation test element of the present invention, which is preferably produced in strip form, can easily be prepared by processes to those of ordinary skill in the arts of printing, punching, and laminating. The design of the coagulation test element allows a simple and cost efficient production process, which is preferably but not necessarily of a continuous nature. 
     In a first step of the preparation method, a pattern of the sample distribution system  6  is formed by creating areas of high and low surface energy on a substrate. In a first embodiment, the areas of high surface energy forming the sample pathways  6   b  and detection areas  6   a ,  6 ′ a  on the first and second surfaces  2   a ,  4   a  are created by applying a hydrophilic formulation on a hydrophobic surface of a substrate. As detailed above, it is also possible to create the areas of high and low surface energy by applying a pattern of hydrophobic “guiding elements” on a hydrophilic surface. In the preferred case the substrate has an intermediate hydrophobic character of commercially available transparent polymer films, whereby areas of low and high surface energy of the sample distribution system and sample detection areas are created by printing the hydrophilic pathways underneath or surrounded by the hydrophobic pattern of the hydrophobic guiding elements. 
     The substrate may be formed of a material like glass, polyvinyl acetate, poly-methyl-methacrylate, poly-dimethyl-siloxane, polystyrenes, polyesters and polyester resins containing fluorene rings, polycarbonates and polycarbonate-polystyrene graft copolymers, terminal modified polycarbonates, polyolefins, cycloolefins and cycloolefin copolymers, and/or olefin-maleimide copolymers. 
     The application of a hydrophilic pattern on a hydrophobic substrate and/or the application of hydrophobic “guiding elements” on a hydrophilic substrate or any combination of it can be accomplished with flexography, lithography, gravure, solid ink coating methods, or ink-jet-printing processes. 
     However, the preferred fabrication method is flexography, which allows high-resolution printing on rotary presses and supports high-speed production. It is an established technology for printing on polymer film substrates and widely used in, the packaging industry. The optical detection process shown in  FIGS. 8   a  and  8   b  requires transparent and clear ink with low viscosity for the hydrophilic pattern. Low viscous inks are preferred to achieve a thin and even coating of about 2-4 microns. The optical window of the ink needs to be in the wavelength range suitable for the optical detection of the chemical reaction. The requirements for hydrophobic inks, apart from the hydrophobic nature, are less stringent and could be used to decorate the coagulation test element with a desired colour as well, thus non transparent inks are preferred for this step. The operation of a four-colour flexography-printing machine is established practice and provides no operational problems. The same holds for lithography device. 
     Most convenient for the preparation of the coagulation test element are solvent based inks, which are available in a large variety from various manufactures. Further, all such available inks could be fine tuned with additional additives and pigments to optimise the required parameters. Many of these inks are based on nitrocellulose ethanol or poly vinyl butyral ethanol mixtures and can be obtained e.g. form Sun Chemicals Inc. (35 Waterview Boulevard, Parsippany, N.J., USA) or Flint Ink Inc. (4600 Arrowhead Drive, Ann Arbor, Mich., USA). 
     Even though solvent based or UV curing inks are applicable to prepare the coagulation test element, electron beam (EB) curing inks have some preferred properties. These inks provide highest resistance to mechanical and chemical factors, and contain 100% polymers, optionally with pigments, but no volatile organic solvents and photo initiators, which have proven to affect the stability of sensor chemistry. These positive gains in performance characteristics are derived from the ability of electrons to form cross-linked polymeric films and to penetrate the surface. 
     Inks used in EB curing make use of the polymerising capability of acrylic monomers and oligomers. Acrylic chemistry has a special significance in modern day inks. (6 J. T. Kunjappu. “The Emergence of Polyacrylates in Ink Chemistry,” Ink World, February, 1999, p. 40.) The structure of the simplest acrylic compound, acrylic acid, is shown in the formula (I): 
       CH2=CH—COOH  (I) 
     The double bond in the acrylic moiety opens up during interaction with electrons (initiation) and forms a free radical that acts on other monomers forming a chain (propagation) leading to high-molecular-weight polymers. As mentioned before, radiation induced polymerisation requires no external initiator since radiation itself generates free radicals with the result that no initiating species will be left in the coating. 
     A variety of acrylic monomers are available for EB curing that range from simple acrylates such as 2-phenoxyethyl acrylate and isooctyl acrylate, to pre-polymers like bisphenol A, epoxy acrylate and polyester/polyether acrylates (R. Golden. J. Coatings Technol., 69 (1997), p. 83). This curing technology allows the design of “functional inks” with the focus on the desired chemical and physical properties without the necessity of a solvent and curing chemistry required by other inks, which may complicate the design process. 
     Generally suitable hydrophobic inks might contain monomers, oligomers, and pre-polymers with hydrophobic functions like isooctyl acrylates, dodecyl acrylates, styrene or silicon derivates, systems with partly fluorinated carbon chains, and additional hydrophobing additives and/or fillers such as hydrophobing agents belonging to the TEGO Phobe Series (TEGO Chemie Service, Essen Germany), hydrophobic pigments such as copper phthalocyans, carbon, graphite, or hydrophobic fillers such as silicon modified fumed silica or PTFE powders and PTFE granulates. Due to the vast variety of additives, pigments, and fillers the above suggested compounds will only have exemplary character. 
     Inks with hydrophilic functions can be realised from a wide selection of ethanol and water-soluble polymers and polymer mixtures thereof. Useful are polymers and polymer derivatives, copolymers and compounds base on alginate, cellulose and cellulose ester, hydroxyethyl cellulose, gum, acrylic acid, polyvinylalcohol, polyethylene-glycol, polyethylene-oxide, vinylpyrolidone, polystyrene sulfonate, poly(methyl vinyl ether/maleic acid), vinylpyrolidone/trimethylammonium copolymers, and alkyl-phosphocholine derivates. Further optimisation can be achieved with organo-modified silicone acrylates additives, which are a cross-linkable species of organo-modified polysiloxanes, and fluorinated surfactants. A general suitable coating provides a contact angle with water of typically less than 35° and a surface energy of typically more than 50 mN/m. 
     The second step of the production process comprises the application of the coagulation formulations, containing the coagulation stimulating reagent and additional agents to produce a printable and/or dispensable ink forming a uniform layer within the sample detection areas. 
     In a preferred embodiment, the amount of thromboplastin on first surface  2   a  of base layer  2  is precisely dosed using a suitable method such as ink jet printing. Indeed it would be obvious to those skilled in the art that other dosing techniques could be utilised for the purposes of this invention. 
     On all corresponding sample detection areas of the opposing surface will be furnished with the required quality control formulations containing the appropriated amount of alginate or another coagulation accelerator, EDTA or other coagulation inhibitors, and the fluorescent molecular rotor as detection aid if required for the anticipated detection regime. 
     Since the concentration level respectively the total amount of the coagulation stimulating reagent applied to the predetermined sample detection areas  6 ′ a   1  to  6 ′ a   3  is responsible for the sensitivity and dynamic range of the various discussed coagulation test elements, as well as the concentration level and precision of the applied quality control compounds is responsible for the accuracy of the test results, it is paramount for this application to provide coagulation test elements with a precise dosage of the above elements, compounds, and ingredients. Such precise dosage can be implemented for example using a micro dispenser system (e.g. available from Vermes Technik GmbH &amp; Co. KG, Palnkamer Str. 18-20, D-83624 Otterfing, Germany). The coating formulations must be prepared to be highly soluble by the liquid sample medium to allow a fast and residue free reconstitution after the introduction of the sample fluid. 
     The next step comprises the lamination procedure, in which the base and cover layer presenting the first and second surfaces of the sample distribution system are laminated onto a centre layer, thereby defining a distance between the first and second surface of the base and cover layer. The centre layer provides a discontinuity to create a cavity for the sample distribution system in the areas where the sample distribution system is formed on the first and second surface of the base and cover layer. The patterns of high and low surface energy formed on the first and second surface of the base and cover layer must be aligned to be mostly congruent to enable the formation of a functional sample distribution system between the first and second surface. 
     Precise xy-registration of base and cover layers becomes a critical task for the function of the element, if this registration is not achieved, the sample distribution system will not function properly and/or will have a higher variability with regards to the specified sample volume. Registration tolerances should be within +/−5% of the width of the hydrophilic pathways to achieve good performance. 
       FIG. 13  shows the top view (left) and cross-section (right) of the coagulation test element and the effect of registration quality. In case of  13   a  the sample distribution system is assembled properly with good alignment of the hydrophilic pathways of the first  2   a  and second surface  4   a . The result of an improperly aligned coagulation test element is given in  FIG. 13   b . Although, the spacer between the base  2  and the cover layer  4  is identical in case of  13   a  and  13   b  the sample volume is falsely enlarged in case b, since the sample fluid covers partly the hydrophobic guiding elements of the sample distribution system. The effect is caused by the sample fluid inside the coagulation test element, which seeks to minimise the surface area exposed to air in order to gain the most favourable energetic state and therefore overriding the effect of the hydrophobic areas. 
     In an alternative embodiment, as shown in  FIG. 13   c , the sample distribution sys-tem of the cover layer  4  is designed about 10% smaller as the sample distribution system of the base layer  2  thus the total sample volume of the coagulation test element is defined by the extensions of the sample distribution system of the base layer, allowing a higher tolerance for the registration process during manufacturing without compromising the precision of the required sample volume. 
     The application of the centre layer, which may be a double-sided adhesive tape with a preferred thickness of 80 microns or alternatively a hot melt adhesive deposited in an equivalent thickness, is less demanding because of the relatively large discontinuity in the material compared to the size of the hydrophilic pathways. Registration is especially important in continuous production lines where the substrate progresses with several meters up to tens of meters per minute. Substrate expansion and web tension make the registration in x-direction (the direction of the web movement) more difficult than the y-direction perpendicular to the web movement. 
     A preparation method for flexible polymer films providing an accurate registration of the patterns of first and second surface is illustrated in  FIG. 14  showing parts of a continuous web production process. In a first production step according to  FIG. 14   a , patterns of the sample distribution system  6  of the base and cover layer are printed on one web substrate  49 , which represents the material of the produced coagulation test elements. As illustrated in  FIG. 14 , the printed patterns of the sample distribution systems  6  are arranged on the web substrates  49  in such a manner that two sample distribution systems are opposite to each other left and right from a mirror line. Optionally, the sample distribution system can be linked in the areas which form the sample application areas. Thus, the position of the predetermined detection areas  6   a ,  6 ′ a  is fixed relative to each other and remains unaffected by the material expansion and web tension. 
     The dotted lines  50  indicate the future cutting lines to segregate the coagulation test elements into strips, while the dotted lines  51  indicate the mirror line of the strip artwork and the future fold line of the web substrate. 
     After printing the flow paths of the coagulation test element, the detection areas  6   a ,  6 ′ a  of the sample distribution system are coated with the required formulations. For example, the detection areas  6   a  of the upper row of the web substrate  49 , which will represent the second surface of the coagulation test element, are coated with the quality control formulations. One of the quality control formulations (e. g. positioned in  6 ′ a   1 ) do not contain active compounds that either inhibit or promote the coagulation reaction and therefore deliver the determined result of the coagulation analysis, whereas the detection areas  6 ′ a  of the lower row of the web substrate  49 , which will represent the first surface of the coagulation test element, are coated with the coagulation formulations containing the tissue thromboplastin to initiate the coagulation reaction. In the special cases other compounds than tissue thromboplastin will be coated on the sample detection areas  6 ′ a , which will trigger and activate the coagulation pathway in different positions to determine the functionality of other coagulation factors. 
     Thereafter, an additionally layer is laminated on one of the surfaces, e. g. the surface  2   a  of the base layer  2 , representing the centre layer  52  of the coagulation test element as shown in  FIG. 14   b . The centre layer  52  may be formed of double-sided adhesive tape or a hot melt adhesive, which provides breakthroughs  5  exposing the sample distribution systems  6  to create cavities for the sample distribution systems in the coagulation test elements after the final assembly step. 
     The coagulation test element of the present invention is then assembled by folding the two sides along the mirror line  51 , e. g. with help of a folding iron or other suitable equipment, as illustrated in  FIG. 14   c  creating a folded and laminated web  53  as shown in  FIG. 14   d . Subsequently, a press roller can secure a tight connection between the centre layer, base and cover layer. 
     Finally, the laminated web  53  is cut or punched in to the desired product shape, whereas line  50  projects an exemplary shape of the final coagulation test strip onto the web  53  before the segregation process. With the preparation method illustrated in  FIG. 14  the top part of the substrate can be folded on to the bottom part without the danger of loosing the registration in the x-direction of the web and provides an easier method to get the right registration of the first and second surfaces forming the sample distribution system in comparison to single sheet process. 
     It will be obvious for someone skilled in the art that base and cover layer are exchangeable in the discussed embodiments without affecting the principle of the invention. 
     This invention provides a test system for determining the coagulation characteristics of plasma and whole blood samples consisting of a coagulation test element and a small and simple hand held meter device suitable for home and point of care settings. The coagulation test element is provided with an integrated quality control system suitable for dry reagent test strip format with a very small sample volume of about 0.5 μL. The production of the inventive coagulation test element involves only a small number of uncomplicated production steps enabling an inexpensive production of the element.