A new chemiluminescence immunoassay for triiodothyronine and thyroxine: evaluation using quality control sera assayed in an interlaboratory survey.

A recently developed chemiluminescence immunoassay system (LIA-mat) for triiodothyronine and thyroxine, set up by Byk-Sangtec Diagnostica (Dietzenbach, Germany), has been evaluated and compared with radioimmunoassays and with a chemiluminescence enhanced enzyme immunoassay (Amerlite), using control materials circulated in a national interlaboratory quality control, as well as patient sera. The LIA-mat assays are competitive methods which use coated monoclonal antibodies and triiodothyronine- or thyroxine-ABEI (aminobutylethylisoluminol) conjugate as tracers. The working range of LIA-mat T3 (computed from the within-assay precision profile) extended from 1.4 to 12.3 nmol/l; the between-assay precision was 8.1 - 19.3 CV%. Regression analysis of the LIA-mat T3 results (y) against the consensus means (x) of the participants in the national interlaboratory survey yielded: y = -0.14 + 1.05 x, r = 0.95. The working range of LIA-mat T4 extended from 33 to 515 nmol/l; the between-assay precision was 5.4 - 9.2 CV%. An excellent agreement was found between LIA-mat T4 results (y) and the consensus means (x) of the laboratories participating in the national interlaboratory survey (y = 3.79 + 1.02 x, r = 0.98).