Clinical and laboratory evaluation of a commercial kit for measurement of serum free thyroxin ("Amerlex Free T4").

Different indexes of thyroid function were determined in conjunction with values obtained with a new commercial radioimmunoassay kit for serum free thyroxin, in 49 apparently healthy subjects, 87 pregnant women, and 142 outpatients attending the thyroid clinic. The results indicate a diagnostic success rate of 88% when free thyroxin was measured instead of estimating the so-called free thyroxin index. Furthermore, in three cases of papillary carcinoma the concentration of free thyroxin was increased, although all the other laboratory tests indicated a euthyroid state. Technically, the method is simple, rapid, and precise, and it would be of most value in the small hospital laboratory lacking the facilities of a comprehensive thyroid-function test service.