MATRIX EFFECTS IN THE RADIOIMMUNOASSAY OF ESTRADIOL AND TESTOSTERONE IN PLASMA OF VEAL CALVES AND HOW TO AVOID THEM

Within the scope of the control of the illegal use of naturally occurring steroids in veal calves, an evaluation was made of two commercially available kits for the determination of estradiol-17beta and testosterone in plasma. Four radioimmunoassay (RIA) kits, two with and two without extraction, used in human medicine were evaluated and eventually adapted for the assay of bovine plasma samples. On measuring estradiol-170 lower values were obtained when the plasma samples were assayed without extraction (I-125-RIA). This difference was due to a plasma matrix effect which could be avoided by using either the extraction method (H-3-RIA) or by dissolving estradiol standards in bovine plasma instead of human serum. This plasma matrix effect did not interfere as much when testosterone levels were measured. However, the best method for the determination of both steroids in bovine plasma was RIA with extraction (H-3-RIA).