EFFECTS OF HEMOLYSIS, LIPEMIA AND BILIRUBINEMIA ON AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR CORTISOL AND FREE-THYROXINE IN SERUM SAMPLES FROM DOGS

The possible interference of haemolysis, lipaemia and bilirubinaemia o n commercially available enzyme-linked immunosorbent assays (test kits Enzymun-Test; Boehringer Mannheim) for cortisol and free thyroxine (F T4) in canine plasma samples was studied. Serum samples from 20 clinic ally normal dogs were enriched in vitro with different amounts of fres h haemolysate, lipid and bilirubin and compared with the original sera . The tests were used in connection with the analyser system Enzymun-T est (Boehringer Mannheim) System ES300. Haemolysis significantly (P=0. 039) interfered with the accuracy of FT4 determination independent of haemoglobin concentrations. Thus, haemolysis should be avoided in FT4 testing by competitive enzyme immunoassay. Lipaemia significantly inte rfered (P=0.0015) with cortisol determination but not with FT4 determi nation (P=0.41). Regression analysis showed that FT4 concentration sig nificantly increased as triglyceride levels increased, especially at c oncentrations greater than 12 mg dL(-1). The positive bias observed wa s of no diagnostic importance for cortisol results and the increase of FT4 levels could be precisely predicted by linear regression analysis . The addition of bilirubin significantly (P=0) interfered with cortis ol testing but, as with lipaemia, the magnitude of the differences wer e of no clinical significance.