Free Thyroxine: An Abbreviated Practical Assay

Abstract

A simplified, reproducible procedure for the determination of serum free thyroxine has been developed. Diluted serum labelled with thyroxine ¹²⁵I (T₄-¹²⁵I) was subjected to 3½-hour dialysis at 36 C , with subsequent purification of the dialysate with protein-coated charcoal. The results were in agreement with those obtained by overnight dialysis for a normal population, women taking oral contraceptives, or pregnant, hypo- and hyperthyroid patients and “sick” euthyroid subjects. The main advantages are the elimination of bacterial contamination, ease of dialysate purification, and rapidity of performance, since a technologist can complete the procedure in one working day for 20 to 25 specimens of serum in duplicate.