DETERMINATION OF FREE TRIIODOTHYRONINE BY 6 DIFFERENT METHODS IN PATIENTS WITH NONTHYROIDAL ILLNESS AND IN PATIENTS TREATED WITH AMIODARONE

We performed a methodological comparison of free triiodothyronine (FT3 ) estimates in patients with liver cirrhosis and renal failure. Patien ts were classified in terms of severity of illness on the basis of the ir total triiodothyronine, total thyroxine and reverse triiodothyronin e profiles. FT3 levels, measured in direct dialysis, microchromatograp hy, labelled analogue and two-step immunoextraction assays were signif icantly (P<0.01) lower than the control group in all patient categorie s. However, FT3 measured by a labelled antibody radioimmunoassay was s ignificantly reduced only in the most severely ill sub-group of patien ts, In a further group of patients on long-term amiodarone therapy for cardiac disease all FT3 methods, with the exception of the labelled a ntibody radioimmunoassay and an analogue method, yielded significantly (P<0.01) reduced levels. A significant negative association between F T3 and subject age was demonstrated for all methods except the labelle d antibody radioimmunoassay, and a weak but significant negative corre lation between log thyrotropin and FT3 was only seen with this assay. Three methods demonstrated a correlation (P<0.02) with albumin levels in patients with the 'low T3 syndrome'. In this group, albumin had a p redictive value (P less than or equal to 0.02) for four out of six ass ays as determined by stepwise variable selection. Our findings suggest that users of FT3 assays should exercise caution in interpreting resu lts in non-thyroidal illness and amiodarone treated patients, as there are method-related differences in the profiles obtained.