Performance characteristics and diagnostic value (vs other tests) of two radioimmunoassay kits for estimating free triiodothyronine in serum.

Abstract

We compared the clinical value of "Amerlex" (Amersham International) and "Pre-release Coat-A-Count" (Diagnostic Products Corp.) radioimmunoassay kits for free triiodothyronine with that of triiodothyronine, triiodothyronine/thyroxin-binding globulin ratio, and free triiodothyronine index in patients with thyroid disease, pregnant women, oral contraceptive users, thyroxin-binding globulin-deficient subjects, and patients receiving phenytoin. Assay of free triiodothyronine in hyperthyroidism provided diagnostic information similar to that from the indirect indices, whereas the free triiodothyronine index was the most sensitive index of hypothyroidism. With respect to diagnostic value, free triiodothyronine assay was comparable with the free triiodothyronine index and superior to triiodothyronine assay and the triiodothyronine/thyroxin-binding globulin ratio in correcting for alterations in thyroid-hormone binding capacity. In neither kit for free triiodothyronine was the equilibrium between bound and free hormone significantly disturbed during assay. Overall, as a diagnostic index of thyroid status, free triiodothyronine is as good as the free triiodothyronine index and better than either triiodothyronine or the triiodothyronine/thyroxin-binding globulin ratio.

Amerlex free triiodothyronine and free thyroxine levels in normal pregnancy

“…The results found for FT, in pregnancy show a very similar pattern to those for FT,; again two results (4%) in the 2nd trimester, but only 25 (42%) in the final period fell below the non-pregnancy reference range. These results are in accordance with those of Wilke et al (1984) and Amersham (kit package insert) but not with those of Franklyn et al (1983a), Amino rt d. (1983) and Nasralla etal. (1983).…”

The Evaluation of Free Thyroid Hormones (FT4 and FT3) in the Routine Diagnosis of Thyroid Function

“…This range has also been stated by the manufacturing firm and has been confirmed by the results of a multicentre study (11). Lower normal reference intervals (4.5 to 7.9 pmol/1) were calculated by Wilke et al (25). In the euthyroid population 3 FT3 values (between 10-12 pmol/1) were over the 95% confidence limits, while 2 FT3s (3-4 pmol/1) were below it ( Fig.…”

“…The results of large scale investigations have confirmed the advantages of free thyroxine measurements in the diagnosis of thyroid function (4,8,10,13). The advantages of the determination of free triiodothyronine by the same methods are at present still being scrutinized (9,11,19,25).…”