Radioimmunological assays for triiodothyronine(T 3) or thyroxine(T 4) in sera containing antibodies against the hormones

For serum samples containing antibodies in vivo against triiodothyronine or thyroxine, the radioimmunoassays in use may give highly erroneous results. We wanted to compare the effects of two different radioimmunoassay systems on such sera, and to develop a suitable extraction procedure for use before such assays. Very different results were obtained with the use of single antibody or double antibody techniques on unextracted sera. The highest recoveries of total T 3 and T 4 from sera were found with two successive ethanol extractions. These reports of the binding of T 3 and T 4 seem to indicate that abnormal binding of thyroid hormones happens more often than was previously believed. The possibly misleading values obtained by radioimmunoassays on such sera indicate the need for a reliable method that eliminates the interference caused by the antibodies during the assay. Some attempts have been made to investigate the total T 3 or T 4 concentrations when binding to gamma globulin fractions has occurred (9, 10, 11), but we found these methods difficult to reproduce. Our intention is to show the different values obtained with antibody-containing sera against T 3 using two radioimmunoassay systems, and to investigate the ability of different procedures to extract T 3 before a radioimmunoassay.