INTERNATIONAL AND REGIONAL STANDARDIZATIO N OF IMMUNO-ENZYME TESTS - METHODS, ADVANTAGES AND LIMITATIONS

Numerous attempts have been made to standardise immune-enzyme techniqu es (enzyme-linked immunosorbent assay: ELISA) used for the diagnosis o f infectious diseases, in order to improve the reproducibility of the tests, expression of results, choice of a positive threshold, and sele ction of reference samples. The international standardisation of reage nts and test protocols appears essential for quality central and the c omparison of results between laboratories, but the interpretation of r esults can encounter major differences depending on the geographical s ector under study. Based on these studies, and in the light of a model indirect ELISA for detecting antibodies against Trypanosoma vivax in cattle, the author proposes the international standardisation of reage nts, test protocol, and the expression of results of ELISA using inter national reference samples. For local standardisation, the following p roposals are made: - sampling of representative local populations - es tablishment of the distribution patterns of infected and uninfected lo cal populations - selection of representative controls from local popu lations (secondary reference samples) - expression of test results in comparison with these controls - establishment of internal quality con trol based on the response of controls - determination of a positive t hreshold, in accordance with the requirements of the user - adaptation of the positive threshold according to the prevalence observed in the geographical sector under study. These measures will make it possible to determine sensitivity and specificity of the test in the populatio n studied and, when the prevalence of infection is known, to calculate the predictive values of the test.