EVALUATION OF AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR THE DETERMINATION OF FREE-THYROXINE IN CANINE PLASMA SAMPLES ASSISTED BY DATA ON BIOLOGICAL VARIATION

The purpose of the present study was to evaluate a commercially avalia ble enzyme linked immunosorbent assay (ELISA) for the determination of the free thyroxine (FT4) concentration in canine plasma samples. The test kit Enzymun-Test(R)(Boehringer Mannheim) for determination of FT4 concentrations in human serum and plasma was used in connection with the analyzer Enzymun-Test(R)(Boehringer Mannheim) System ES-33 by foll owing the assay protocol suggested by the manufacturer. To assist in t he evaluation of the ELISA method, goals for the precision of the assa y were established from the inter- and intraindividual coefficients of variation estimated from determination of the plasma FT4 concentratio n in blood samples collected weekly from 8 healthy dogs for a period o f 4 weeks. The intra- and interassay coefficients of variation ranged from 6 % to 13 %, the proposed goals for the precision ranging between 10 % and 15 %. The detection limit of the assay was 2 pmol/l which is well below the FT4 concentration commonly observed in plasma from dog s, and the FT4 concentrations determined in plasma from healthy dogs w ere comparable to those reported in the literature. Hence, the ELISA m ethod evaluated in this study offers a precise and accurate measuremen t of the FT4 concentration in canine plasma samples, the inter- and in traassay precision comparing favorably to the proposed specifications for assay precision using estimates of the inter- and intraindividual coefficients of variation.