Clinical Evaluation of Two Calculation Methods for a Free Thyroxine Assay

A commercial assay for the measurement of the free thyroxine concentration in serum has been subjected to a change of method of calculation, together with a change of antibody. The clinical significance of both methods of calculation, before and after the change of antibody, has been investigated. Before the change of antibody the results of the original method of calculation were in slightly better agreement with the clinical data. After the change of antibody the results of the modified method of calculation were in better agreement with the clinical data.