Laboratory evaluation of an immunochemiluminometric assay of triiodothyronine in serum.

We evaluated an immunochemiluminometric assay for total triiodothyronine (T3) in serum. Acridinium ester is used as chemiluminescent label, with magnetic particle separation. Intra-run precision was demonstrated by CVs of 8.6%, 8.1%, and 4.4% at T3 concentrations of 1.3, 2.2, and 4.3 nmol/L, respectively. Between-run CVs were 19.1%, 8.8%, and 6.9% at respective T3 concentrations of 0.9, 2.4, and 6.2 nmol/L. We tested the validity of a two-point calibration system by comparing it with a set of 10 calibrators; use of the latter only minimally improved assay precision. The central 95% reference range, determined by data from 109 healthy blood donors, was 1.5-3.2 nmol/L. Comparison with a standard radioimmunoassay method revealed constant error, attributed to bias or matrix effects between the different calibrators used in the two assay systems. Assay time for 60 samples was 2.5 h. We conclude that this assay is rapid and precise, and offers safety and time advantages over conventional RIA techniques.