MEDICAL TESTING DEVICE

Abstract: A disposable medical testing device (17) adapted to be held against the skin of a patient, which enables the performance of skin testing for the diagnosis of both immediate hypersensitivity and delayed hypersensitivity immune reactions. The device is comprised of a hollow body with a sealed chamber in which is mounted a movable needle (3) capable of penetrating a patient's skin to a predetermined depth and a test reagent container (2). The device (17) is manipulable by a user to reduce the volume of the chamber and moving the needle thus releasing the reagent and causing penetration of the skin. The released reagent is delivered to the skin penetration site, and any resulting skin reaction is observed and recorded. Embodiments of the invention marked with a calibrated scale and details of patient and test date which allow multiple antigen tests to be performed are also disclosed. A method of testing for immune response using the device (17) is also disclosed.

Description: Medical Testing Device TECHNICAL FIELD The present invention relates to a novel disposable testing device for skin testing human subjects for immediate hypersensitivity (allergic ) or delayed hypersensitivity (cell-mediated) immune reactions. The testing device comprises one or more separate needles each in combination with a small reservoir of antigen test reagent in a strip, sheet or patch format. BACKGROUND ART Skin testing for allergy has conventionally been performed by putting a small drop of the suspected allergen on the back or the forearm of the subject and then exposing the underlying tissue by pricking the skin with a needle. An inflammatory response occurring within about 10-15 minutes indicates allergy to the suspected substance. Commonly, allergy to between 5 and 20 suspected substances may be tested in this way at any one time. This test commonly called the "skin-prick test", has remained essentially unchanged in its design since it was first introduced over 70 years ago. The method, still widely used by specialists in the field of allergic disease, is not as popular with general practitioners since it takes up valuable consultation time in the surgery, is uncomfortable for the subject and is costly to provide, especially if it is only done occasionally. Prick testing also requires some technical skill and is quite labour intensive. However, it is the most reliable method of those used to diagnose allergy and gives a result within 10 to 30 minutes of starting the test. In a similar manner, testing for cell-mediated immunity may be performed by either injecting a small quantity of antigen under the surface of the skin using a needle and syringe or by puncturing the skin and allowing antigen solution to passively infiltrate the puncture site. The skin reaction, which is an index of the patient's ability to mount an immune response to the test antigen, is usually measured many hours to several days later. In the last 15 years, an alternative method of testing for allergy using an j_n vitro assay has been introduced. The assay requires the use of serum, the reagents used are costly, assays are only performed by specialist pathology laboratories, and several days may elapse before a result is known. Because of the cost, the number of tests which can be performed is often limited to 4 suspected allergens. Only in rare circumstances do such j_n vitro assays offer any advantages over skin tests, for example where the skin of a patient with eczema is highly inflamed, or when the patient is taking a particular drug which interferes with the skin test response. The correlation between results from skin prick tests and in vitro tests is only about 707o and there are several reasons why such in vitro tests sometimes produce false negative and false positive reactions. Despite this, these assays are very popular (well over 100 million have been performed internationally), and despite several more companies entering the field recently and the introduction of minor changes in design and/or procedure, no major improvements have been made. It would be desirable to adapt the skin test to make it more available and acceptable to both patient and physician, and to improve the speed and reliability of the diagnosis of immune-mediated responses. Reduction of the costs of both tests would also, of course, be welcome. An object of the present invention is to refine the existing methods of skin testing for the diagnosis of both immediate and delayed immune reactions. The procedure when the device of the present invention is employed does not require any specialized technical expertise and is sufficiently simple to be used, without specialised training, by general practitioners (GPs). It is also more acceptable to patients than when conducted according to prior art techniques. DISCLOSURE OF THE INVENTION In accordance with the present invention there is provided a medical testing device adapted to be held against the skin of a patient to perform a test, said device comprising a hollow body providing a sealed chamber, a needle mounted within said chamber and movable to extend beyond said body to penetrate a patient's skin to a predetermined depth, a test reagent within said chamber, and wherein said device is manipulable by a user to reduce the volume of said chamber to release said reagent and to cause penetration of said needle by moving the needle to extend beyond said body. In another aspect, the invention provides a method of testing for an immune response, which method comprises applying to the skin of a patient a medical testing device adapted to be held against the skin, said device comprising a hollow body providing a sealed chamber, a needle mounted within said chamber and movable to extend beyond said body to penetrate a patient's skin to a predetermined depth, a test reagent within said chamber, and wherein said device is manipulable by a user to reduce the volume of said chamber to release said reagent and to cause penetration of said needle by moving the needle to extend beyond said body, manipulating said device to release said reagent on to the skin and to cause penetration of the skin by said needle, observing and recording any skin reaction resulting therefrom after an appropriate time interval. Generally, the needle will be adapted to penetrate the skin about 1 to 2mm and may have a plurality of points or be fluted or grooved to enhance flow of the reagent to the skin. To limit the depth to which the needle penetrates the skin, it may be fitted with a collar or be of enlarged cross-section beyond its point or points. In general, the reagent will be an antigen. However, other components or other reactive compounds may be included in the reagent. Different substances, or dilutions of the same substance with or without control substances such as the vehicle alone, or standard solutions, such as a histamine solution, may be tested concurrently at different skin sites, when the medical testing devices of the invention are incorporated into strips or sheets. Individual patches, strips or sheets may be manufactured as part of a large sheet and separated into single patches, strips or sheets prior to use. In a format where multiple tests are involved, sufficient distance would be allowed between individual antigen/needle units to avoid one test substance interfering with an adjacent test substance. For example, in skin testing for immediate hypersensitivity, a minimum distance between units would be about 20mm. The reagent may be conveniently contained within a capsule, reservoir or porous matrix or may contain an additive to form a paste or gel. It is preferred to include a transparent layer in the device of the invention to both identify the reagent and to record details of the test. Thus, the transparent layer may be printed with identifiers of both the subject tested and of the test substances employed. It is preferably of a material which can be written on and has calibrations to enable the size of the skin reaction to be measured. It is preferably coated on the underside with a low-tack adhesive to secure the device to the skin in use. The adhesive also permits the transparent strip to be affixed to the patient's medical records. After placement of the strip or patch on the skin, light direct finger pressure on each unit both releases the solution containing the antigen and causes the needle to penetrate the skin to a limited depth insufficient to draw blood. The antigen solution then infiltrates the site of the needle puncture causing a limited exposure of the intrader al or subcutaneous tissues to the antigen. The immunological response to such exposure is determined after the appropriate time, depending on the immune response involved. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a cross section of the skin test device in accordance with a first embodiment of the invention. Figure 2 shows a second embodiment in cross section. Figure 3 shows an alternate arrangement of a needle unit applicable to the invention and illustrated in a third embodiment. Figure 4 shows a cross section of fourth embodiment of the invention. Figure 5 shows a fifth embodiment in cross section. Figure 6 shows various designs of needle points which can be used in the test devices of the invention. Figure 7 shows the view from above of patch-like embodiments of the invention. Figure 8 shows a view from above of the arrangement of a test device of the invention including a number of antigen testing units Figure 9 is a side view of the embodiment of Figure 8. Figure 10 is an exploded enlarged view of one of the antigen testing units of Figures 7, 8 and 9. Figure 11 shows a view from above of the transparent layer of the test device of Figures 8 and 9. BEST MODES FOR CARRYING OUT THE INVENTION The following description relates to preferred embodiments of the invention as illustrated in the accompanying drawings and should not be construed as limiting on the claims. The skin test device (17) of Figure 1 is made up of an antigen support layer (12) containing one or more (1 illustrated) capsules (2) containing antigen solution (1). Disposed to one side of the layer (12) is a compressible layer (11) and a cover (14). The layer (11) could be made of foam plastic, rubber or be of an air cell construction, and is adhered to support (12) and cover (14) is adhered to layer (11) by means of high-tack adhesive (15). The compressible layer (11) keeps capsule (2) and needle ( 3) separate when the device (17) is not in use, and keeps the needle above the plane of the patient's skin when uncompressed. It can also provide a physical mattress to house the capsule (2) and the needle ( 3 ) . The cover (14) incorporates a needle (3) and ensures sterility and adds rigidity. The cover may be made of a material such as plastic, impregnated paper or metal foil. Its upper surface may be colour-coded and/or printed with the name(s) of the antigen(s) and with instructions for use of the device. Alternatively, it may be decorated to render the device more acceptable to children. The needle (3) which ruptures the capsule ( 2) prior to the needle penetrating the skin is provided with a collar (7) to restrict the depth of penetration of needle (3 ) into the skin, preferably to about 1 to 2mm, when the device (17) is in use. A transparent layer (10) and bottom cover (9) are disposed on the side of the support layer (12) opposite the needle (3) with a hole (18) in line with the needle ( 3 ) . The bottom layer (9), seals, protects and ensures the sterility of the unit. It is removed prior to the start of the test. The removal of this layer exposes a layer of low-tack adhesive (16), shown bonded to the transparent layer (10). The purpose of the adhesive is to temporarily and lightly hold the device to the surface of the skin. The adhesive concerned should not be strong enough to cause discomfort when the device is removed from the skin. Layer (10) is also secured to support layer (12) by means of low-tack adhesive (16). The layer could be made of plastic, cellulose, nylon or other transparent material which can be written on to outline the extent of a skin reaction and to record details of the subject - for example the name, unit number and date. This layer could also be printed with scale markings in mm to enable a skin reaction such as a wheal or flare response to be measured. Low-tack adhesive (16) permits the upper layers to be removed to allow the skin reaction to be viewed through the remaining transparent layer. When the skin reaction has fully developed, it can be measured from the scale or the outline of the reaction can be marked on the transparent layer which may then be removed and kept for record purposes. In the embodiment of Figure 2, needle guides (8) are built into top layer (14). The needle (3) is adapted to fit guide (8 ) tightly by means of collar (7). Needle guide (8) also locates capsule (2) of antigen solution (I) between needle (3) and hole (18) in transparent layer ( 10 ) . The device is sealed by bottom cover (9). Both top cover (14) and -bottom cover (9) are affixed to transparent layer (10) by low-tack adhesive (16 ) . Figures 3 and 3a illustrate a further embodiment of the invention where as in the embodiments of Figure 1 and 2, a transparent layer ( 10) is bound to bottom cover (9) and the balance of the device by low-tack adhesive (16). In the embodiment of Figures 3 and 3a co pressive layers ( II) are provided above and below a support layer (13) which holds modified needle (3') and locates needle (3') above hole (18) in transparent layer (10). Compressive layer (11) away from the transparent layer ( 10 ) is thicker than the compressive layer (11) adjacent transparent layer (10) and carries capsule (2) of antigen solution (1) and locates it above needle (3') and hole (18). Needle (3 l ) carries barbs (4 ) opposite the needle point which enable capsule (2) to be pierced to release the antigen solution (1). The device has a top cover (14). Layers (14) and (11 ) (thick), (11) (thick) and (13), and (13) and (11) (thin) are bound together with high-tack adhesive C15). In the embodiment of Figure 4, the antigen solution (1) is contained in a reservoir (5) so shaped to correspond with a hub (19) in needle ( 3 ) . Needle (3) has a hollow shaft (20) through which the antigen solution ( 1 ) can flow from the reservoir (5) to the skin test site. Needle (3 ) and reservoir (5) are surrounded by compressible layer (11) and covered by a top covering layer (14). The needle and reservoir are aligned over a hole (18) in transparent layer (10) which is bound to the compressible layer (11) an to bottom cover layer (9) by low-tack adhesive (16). Figure 5 illustrates an embodiment of the invention similar to that described in Figure 1. In the device of Figure 5, a compressible porous matrix (6), such as glass fibre or plastic foam, containing the antigen solution replaces the capsule (2) and collar (7) of Figure 1. As the capsule (1) is absent, the support layer (12) of Figure 1 is not required in the embodiment described in Figure 5. Figure 6 shows alternative needle configurations which may be used in the skin test device, to enhance the delivery of antigen to the skin, ( a ) depicts a needle with a grooved shaft, (b) depicts a needle with twin points, (c) depicts a needle with multiple points Figure 7 depicts a preferred embodiment of the individual skin test units containing the same single antigen solution arranged in a sheet form, so that the single units can be individually separated. The units of Figure 7 are illustrated in more detail in Figure 10. The antigen solution (1) is contained within a reservoir -into which the needle (3) projects. The top covering layer (14) which could be made of a flexible material such as an ionomer resin, e.g., Surlyn (Registered Trade Mark) is domed at (14 1 ) to provide the space which the needle (3 ) and reservoir (5) occupy. A transparent layer (10) is provided adjacent the reservoir and has a hole (18) to permit the antigen solution to reach the skin when the device is in use. The device is sealed with a bottom layer (9). Figure 8 illustrates a preferred embodiment of the invention where multiple antigen tests can be performed at the same time. A side view of the embodiment of Figure 8 is illustrated in Figure 9. Figure 11 shows greater detail of the transparent layer shown in the previous figures, for the format of the skin test units shown in Figure 8. The embodiment illustrated is marked with a callibrated scale, enabling a skin reaction response to be recorded on this layer along with details of the subject or patient and test date. The volume of antigen associated with each unit is sufficient for a single test. The aqueous solution of the antigen may contain components other than the antigen itself. Such components may be added, for example, to increase the stability of the antigen, reduce the non-specific binding of the antigen to surfaces, maintain solubility, reduce evaporation, protect against contamination by microorganisms or as a buffer. Examples of such added substances include ionic salts, non-reactive carrier proteins such as human serum albumin, non-ionic detergents, glycerol and anti-bacterial and anti-fungal agents. The needle is to be constructed of a material to ensure sharpness, allow sterilisation and be easily manufactured. Some examples of such materials may be hard plastic, steel and nylon. The needle may penetrate the skin with a single point or may possess several points and may also contain features, such as fluting or grooves to improve the flow of the antigen solution into the puncture site. The application of this design may not be restricted to j_n vi o testing of the immune response to antigens. Another application of this device could be the delivery of biological or non-biological material into the skin for purposes other than for diagnosis. Such material could be of microbiological origin to function as a vaccine, immunoreactive material to stimulate an immune response, or a therapeutic drug or other substance. This type of application may require minor modification to the needle. For example, the needle in Figure 4 would have the outlet lower down the shaft towards the point to force more antigen into the puncture site rather than as shown, where the needle is designed to flood the site allowing passive infi ltration. It may also be preferred to incorporate into the layer in contact with the skin, as well as the weak adhesive, an absorbent band between antigen reservoir sites, so that excess antigen solution is not forced from one test site to an adjacent site giving rise to false positive reactions. It may also be preferred to incorporate into the layer in contact with the skin a mild, topical, local anaesthetic which would not interfere with the skin test response, but would reduce the itching and minor discomfort associated with an immediate skin test reaction. Gamma irradiation may be used for sterilisation of the devices of the invention. INDUSTRIAL APPLICABILITY Medical devices of the invention enable allergy and other skin tests to be readily performed by medical and paramedical personnel to provide a quick result and permanent record.

Claims: CLAIMS 1. A medical testing device adapted to be held against the skin of a patient to perform a test, said device comprising a hollow body providing a sealed chamber, a needle mounted within said chamber and movable to extend beyond said body to penetrate a patient's skin to a predetermined depth, a test reagent within said chamber, and wherein said device is manipulable by a user to reduce the volume of said chamber to release said reagent and to cause penetration of said needle by moving the needle to extend beyond said body. 2. The device as defined in claim 1, wherein said predetermined depth is about 1 to 2mm. 3. The device as defined in claim 1 or claim 2, wherein said needle has a plurality of points or is fluted or grooved to enhance flow of the reagent to the skin. 4. The device as defined in any one of claims 1 to 3, wherein the cross section of the needle is enlarged to prevent penetration of the skin beyond the predetermined depth. 5. The device as defined in any one of claims 1 to 4, wherein the test reagent is an antigen. 6. The device as defined in claim 4, wherein the test reagent further contains a stabilizer, preservative or buffer. 7. The device as defined in any one of claims 1 to 6, wherein the test reagent is contained within a capsule or a reservoir. 8. The device as defined in claim 7, wherein the needle is provided with at least one barb opposite its point and the capsule is located adjacent the barb or barbs. 9. The device as defined in any one of claims 1 to 6, wherein the test reagent is contained within a porous matrix. 10. The device as defined in any one of claims 1 to 6, wherein the test reagent contains an additive to form a paste or gel. 11. The device as defined in any one of claims 1 to 10, further comprising a transparent layer, which, in use, is located against the skin. 12. The device as defined in claim 11, wherein the transparent layer is calibrated to enable the test result to be measured. 13. The device as defined in claim 11 or claim 12, wherein the transparent layer is capable of being written on so that the result of the test can be recorded thereon. 14. The device as defined in any one of claims 1 to 13, further comprising a top layer defor able to reduce the volume of said chamber. 15. The device as defined in any one of claims 1 to 14, further comprising at least one collapsible layer which permits the volume of said chamber to be reduced on application of pressure to said device. 16. A plurality of the devices as defined in any one of claims 1 to 15 in the form of a strip or sheet, each said device containing a different reagent. 17. A method of testing for an immune response, which method comprises applying to the skin of a patient a medical testing device adapted to be held against the skin, said device comprising a hollow body - providing a sealed chamber, a needle mounted within said chamber and movable to extend beyond said body to penetrate a patient's skin to a predetermined depth, a test reagent within said chamber, and wherein said device is manipulable by a user to reduce the volume of said chamber to release said reagent and to cause penetration of said needle by moving the needle to extend beyond said body, manipulating said device to release said reagent on to the skin and to cause penetration of the skin by said needle, observing and recording any skin reaction resulting therefrom after an appropriate time interval. 18. The method as defined in claim 17, wherein said predetermined depth is about 1 to 2mm. 19. The method as defined in claim 17 or 18, wherein the cross section of the needle is enlarged to prevent penetration of the skin beyond the predetermined depth. 20. The method as defined in any one of claims 17 to 19, wherein the test reagent is an antigen. 21. The method as defined in claim 20, wherein the test reagent further contains a stabilizer, preservative or buffer. 22. The method as defined in any one of claims 17 to 21, wherein the test reagent is contained within a capsule or a reservoir. 23. The method as defined in any one of claims 17 to 21, wherein the test reagent is contained within a porous matrix. 24. The method as defined in any one of claims 17 to 21, wherein the test reagent contains an additive to form a paste or gel. 25. The method as defined in any one of claims 17 to 24, wherein the skin reaction is recorded on a transparent layer incorporated in the device and located against the skin. 26. The method as defined in claim 24, wherein the transparent layer ibrated to enable the extent of the skin reaction to be measured.

Inventors: BALDO BRIAN ANGELO, TOVEY EUAN ROGER, BALDO, BRIAN, ANGELO, TOVEY, EUAN, ROGER
Applicants: ROYAL NORTH SHORE HOSPITAL, THE ROYAL NORTH SHORE HOSPITAL AND AREA HEALTH SER
Application year: 1988
Main classification: A61B10
IPC codes: A61B5, A61B10, A61B17