Clinical and laboratory studies of time-resolved fluorescence immunoassays of thyrotropin and free triiodothyronine.

We evaluated a new time-resolved immunofluorometric assay (TR-IFMA) for thyrotropin (TSH) and a time-resolved fluoroimmunoassay (TR-FIA) for free triiodothyronine (FT3) in serum. Delfia hTSH Ultra is a solid-phase two-site TR-IFMA involving three monoclonal antibodies directed against different antigenic sites on the human TSH molecule. It offers improved analytical (+3 SD of zero) and functional (10% between-assay CV) detection limits of 0.001 and 0.016 mlU/L, respectively. Results of the assay agreed closely with those of a second-generation immunoradiometric assay (TSH-IRMA) for samples with TSH > 0.2 mlU/L (n = 114). The nonparametric reference interval for TSH in euthyroid men and women was 0.5-4.7 mlU/L (n = 200). The TSH concentrations of hyperthyroid subjects (n = 29) were < 0.016 mlU/L (median; range < 0.016-0.063 mlU/L). The Delfia FT3 assay, a solid-phase TR-FIA, is based on the back-titration principle and second-antibody separation. The parametric reference interval for FT3 in euthyroid men and women was 4.2-7.6 pmol/L (n = 320). The FT3 concentration in hyperthyroidism (n = 29) was 23 +/- 22 pmol/L (mean +/- SD; range 7.9-85 pmol/L). These methods offered rapid results (2-4 h for the whole procedure) and were simple to run.