Clinical comparison of three labeled-antibody immunoassays of free triiodothyronine

Abstract

Three labeled-antibody immunoassays of free triiodothyronine (FT3) were studied in hyperthyroid patients, patients with nonthyroidal illness, and patients being treated with amiodarone; we also studied sera presenting known interferences (n for all groups = 465). The results were compared with those of a one-step labeled-analog assay. The precision of the two automated assays were similar to that of the manual assays. The three labeled-antibody FT3 assays demonstrated a satisfactory diagnostic performance for confirming hyperthyroidism and robustness to interference; nevertheless, two assays displayed unusual behavior in some patients with nonthyroidal illness, with chronic renal failure, or after amiodarone therapy.