DIAGNOSTIC TEST METHOD

Abstract: Carrying out of immunochemical reactions in a test tube having a bottom in the shape of an inverted prism or truncated prism, in such a way that the lower edge of the tube forms a strip having a length which is at least equal to one-quarter of the distance between two opposite walls, or where appropriate to a quarter of the diameter of the test tube, as a result of which both the sensitivity and the readability are improved.

Description: Diagnostic test method. The invention relates to a . method for qualita¬ tively or semi-quantitatively detecting the presence of an antigen or antibody in a test liquid, and also to a test kit which permits carrying out such a method. The diagnosis of pathological conditions in man or animals is frequently carried out by using immuno¬ chemical reactions. In general, the presence of an antigen or antibody in a body fluid is determined i munologically by bringing into contact the corresponding antibody or antigen with the particular body fluid to be tested, usually blood serum or urine. The presence of the antigen or antibody to be detected can then be noted by the fact that a less soluble antigen-antibody complex is formed. Such complexes are formed rather slowly and only at relatively high concentrations of antigen and antibody. It is therefore necessary, in order to increase the sensitivity, to use carriers in order to permit the detection of this type of complex and hence also of the particular antigens and antibodies. The coupling of antigens and antibodies to a carrier is a known technique which is described in all im unological handbooks. Extensively used carriers are, inter alia: erythrocytes, bacterial cells, bentonite, latex particles and cellulose. In the present diagnostic test method, use is made of erythrocytes as carriers. The presence of, for example, an antigen in a test sample or test liquid now be demonstrated by bringing the test sample into contact with anti¬ bodies against this antigen, which are coupled to erythrocytes. If the antigen actually is present in the test sample, an immunochemical reaction will take place between the particular antigen and the antibody which is coupled to erythrocytes, resulting in an antigen-antibody complex coupled to erythrocytes and in a coupling together (agglutination) of such erythrocyte particles; on settling out in a test tube having a round bottom, these agglutinated erythrocytes give a plain light brown pattern. If the antigen is not present in the test liquid, no immunochemical reaction, hence also no agglutination, can take place. The antibody bonded to erythrocytes will settle out after a short time and give a characteristic ring pattern in a test tube having a round bottom. In this test set-up, obtaining a characteristic ring pattern in the test tube therefore means that the suspected antigen is not present in the test liquid, and therefore that the test result is negative. The antigen in question can also be detected in a different manner, namely by bringing the test sample into contact with 2 reagents: (1) the antibody against the particular antigen and (2) the particular antigen coupled to erythrocytes. If the antigen in question is not present in the test liquid, an immunological reaction will take place between the two added reagents, resulting in an agglutination of an erythrocyte-bonded antigen- antibody complex, which on settling out will not give a characteristic ring pattern. If the antigen in question i_s_ present in the test liquid, this antigen will react directly with the antibody, giving a (soluble) antigen-antibody complex, while the unused erythrocyte-coupled antigen will REΛI OMPI settle out after a short time and, in a test tube with a round bottom, lead to the formation of a characteristic ring pattern. In this test set-up, obtaining a characteristic ring pattern therefore means that the test result is positive. Though the interpretation of the test result therefore depends on the chosen test set-up, the characteristic ring pattern of the erythrocyte- bonded antigen or antibody each time forms the basis of the test method. Hitherto, the tests outlined above have been carried out in conventional round-bottomed test tubes. In such test tubes, the characteristic ring pattern of non-agglutinated erythrocytes manifests itself as a more or less thick ring. Surprisingly, it has now been found that carrying out these immunochemical reactions in a test tube having a bottom in the shape of an inverted prism or truncated prism, such that the lower edge of the tube forms a strip having a length which is at least equal to one-quarter of the distance between two opposite walls or where appropriate to a quarter of the diameter of the test tube, (a) assists the readability of the test result, so that significantly fewer incorrect observations are made and (b) increases the sensitivity of the test by a factor of 2 to 3; this means that the antigen or anti- body can new be detected in lower concentrations than is possible with a conventional round- bottomed test tube. The use of the test tube according to the invention can moreover have the optical advantage that the immυnological test can be set up in such a equal to 50-85% of the diameter of the test tube. The depth of the inverted prism (or truncated prism) is not particularly critical; however a preferred "depth" is approximately equal to 25-75% of the diameter of the test tube and more especially 40-50% of the diameter of the test tube. The test method according to the invention can be employed for various types of diagnostic test purposes, for example for the qualitative detection of pathological antibodies in blood or urine, but also for the detection of HCG in urine, as a result of which the test method is particularly suitable as a pregnancy test. OMPI

Claims: Claims 1. Method for qualitatively or semi-quantitatively detecting the presence of an antigen or antibody in a test liquid by bringing this test liquid into 'contact either with an erythrocyte—coupled binding partner of the antigen or antibody to be detected, or with a mixture of an erythrocyte-coupled antigen or antibody itself and the binding partner of the antigen or antibody to be detected, which is not ' coupled to a carrier, and thereafter ascertaining the presence or absence of the antigen or antibody in the test liquid from the characteristic sedimentation pattern, formed in the test tube, of the erythrocytes, characterised in that the test is carried out in a test tube having a bottom in the shape of an inverted prism or truncated prism such that the lower edge of- the test tube forms a strip having a length which is at least equal to one-quarter of the distance between two opposite walls or where -, appropriate to one-quarter of the diameter of the test tube. 2. Method according to claim 1 for detecting the presence or absence of the protein HCG in urine, by bringing a urine sample into contact, in the test tube described in claim 1, with an erythrocyte- coupled anti-HCG and, after 1 to 2 hours, detecting a characteristic sedimentation pattern, in the form of a minus—sign, if HCG is absent in the urine sample. 3. Method according to claim 1, characterised in that the bottom of the test tube has the shape of an inverted truncated prism having a depth of 25-75%, and preferably 40-50%, of the diameter, or where appropriate the distance between 2 opposite walls of the test tube. OMPI - 1 - 4. Test kit suitable for carrying out the process according to one of the preceding claims, which kit comprises at least the following: (a) a test tube having a bottom in the shape of an inverted prism or truncated prism, such that the lower edge of the test tube forms a strip or line having a length which is at least equal to one-quarter of the distance between 2 opposite walls or where appropriate one—quarter of the diameter of the test tube, and (b) the immunological reagents required for carrying out the immunological determination. - fEAlT OMPI

Inventors: SCHEEPENS ANTONIUS HENDRIKUS J, THEUNISSEN HENDRIKUS JOHANNES, VAN HELL HANS, SCHEEPENS, ANTONIUS, HENDRIKUS, JOHANNNES, MARIA, THEUNISSEN, HENDRIKUS, JOHANNES, JOSEPHUS, VAN HELL, HANS
Applicants: AKZO NV, AKZO N.V.
Application year: 1982
Main classification: G01N33
IPC codes: B01L3, G01N33