We compared the clinical value of information on free testosterone as measured with the Coat-A-Count (Diagnostic Products Corp.) radioimmunoassay kit involving a ligand analog with that of total testosterone, the free-androgen index, and free testosterone calculated from concentrations of testosterone, sex-hormone-binding globulin, and albumin, in hirsute women, pregnant women, oral-contraceptive users, women with thyroid disease, and epileptic women taking phenytoin. Total testosterone, the free-androgen index, calculated free testosterone, and free testosterone by RIA were increased in 41-68% of hirsute women. Values for free testosterone increased in the first and third trimesters of pregnancy but remained within normal limits in all non-hirsute groups. Total testosterone was increased in patients having increased sex-hormone-binding globulin, whereas the free-androgen index and, to a lesser extent, calculated free testosterone were significantly decreased. Free testosterone measured by analog RIA not only has greater diagnostic efficiency than total testosterone, it also is technically simpler to determine than the free-androgen index and calculated free testosterone.

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The clinical value of free thyroxine index, thyroxine/thyroxine binding globulin ratio, and free thyroxine concentration were compared in 46 pregnant patients. Overall the free thyroxine index was the best diagnostic index. Pregnancy induced changes in levels of free thyroxine and the thyroxine/thyroxine binding globulin ratio, which gave rise to interpretative problems in some pregnant subjects.

I evaluated Amerlex (Amersham International), Coat-A-Count (Diagnostic Products Corporation), Gammacoat (Clinical Assays), Immophase (Corning Medical), and Liquisol (Damon Diagnostics) radioimmunoassay kits for determinations of free thyroxin concentration in sera. Kit results for free thyroxin and the free thyroxin index and thyroxin/thyroglobulin ratio were compared for patients with thyroid disease and for subjects with normal and altered thyroglobulin binding capacity. Values for free thyroxin, free thyroxin index, and thyroxin/thyroglobulin clearly distinguished hyperthyroid and hypothyroid patients from euthyroid subjects. Each free thyroxin kit showed that fewer euthyroid patients with increased or decreased thyroglobulin binding capacity had values outside of normal limits than was indicated by kits for either free thyroxin index or thyroxin/thyroglobulin. The free thyroxin kits not only provided a better overall index of thyroid status in euthyroid patients who had alterations in thyroglobulin binding capacity than either of the indirect assessments of free thyroxin, but also supplied similar diagnostic information in thyroid disease.

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.