Development and evaluation of a magnetic solid-phase Radioimmunoassay for total human thyroxine (T4)

In this study a simple and rapid magnetic solid-phase radioimmunoassay (RIA) for human thyroxine (T4) was developed using locally raised sheep thyroxine antibody and radioiodinated thyroxine (T4) tracer by chloramine-T method. The assay involves two hours incubation at ambient temperature range (30 to 35 degree C) associated with the antibody covalently linked by the easily performed carbonyldiimidazole (CDI) method to magnetic particles obtained from SIPAC. 0.1 % triton with sodium azide used as a wash buffer. L - Thyroxin Na -salt petahydrate from Sigma was used for the preparation of standards and quality control sera. The coupled magnetic anti-T4 solid-phase titrated in order to find out the suitable antibody concentration (titre) to be used in the assay. Optimizations followed by validation procedures were done. When correlated with kits imported from NETRIA and AMERSHAM, results were found to be highly comparable r = 0.965 and p < 0.05. Shelf life was also studied, so that the local prepared T4 RIA magnetic reagents can be used for the measurement of total human thyroxine with a very low cost compared to imported kits. (author)