Comparison of Laboratory Test Results for Assessing Thyroid Function in Normal Subjects and Treated and Untreated Hyper- and Hypothyroid Patients

Various indexes of thyroid status were measured in sera from normal men and women, normal women who were using oral contraceptives, hyper- and hypothyroid patients, and hypothyroid patients being successfully managed with various forms of replacement therapy. Total circulating thyroxine concentrations were measured by three methods as well as the thyroxine-binding capacity of the serum inter-alpha globulin, "free" thyroxine, and "free" thyroxine index. Our purpose was to compare the various measurements, and to assess their diagnostic usefulness. The most significant finding was that, of 197 hypothyroid patients, all of whom possessed total circulating thyroxine concentrations within normal limits, 28% showed subnormal "free" thyroxine concentrations.