A simple and rapid thyroxine radioimmunoassy (T4-RIA) in unextracted human serum; a comparison of T4-RIA and T4 displacement assay, T4(D), in normal and pathologic sera

Abstract

A simple, rapid and accurate thyroxine radioimmunoassay (T4-RIA) in unextracted serum or plasma has been described, and for comparison T4 determinations have also been made by a T4(D) procedure using Abbott Tetrasorb kits. T4-RIA procedure basically involved denaturation of serum to dissociate T4-protein bond, and T4 released was allowed to react with [125I]T4-labeled T4 antiserum elicited by immunizing rabbits against bovine thyroglobulin. The displaced unbound [125I]T4 was rapidly taken up by an anionic resin sponge within 15 min and this sponge [125I]T4 uptake was linearly related to T4 present in standards or serum. The denaturation of serum effected by trichloroacetic acid-sodium hydroxide permitted virtually 100% T4 extraction recovery in normal, pregnancy, hypo- and hyperthyroid sera whereas 72.9-87.6% T4 recovery from normal serum (and with large individual differences) was noted with lower alcohols in T4(D) procedure. Cumbersome and/or tedious steps such as pre-extraction, centrifugation, time consuming bound and unbound hormone separation procedures, etc. are obviated in T4-RIA and the entire assay can be completed in the same tube in approximately an hour. These attributes along with increased sensitivity and specificity and the need for only microamounts of test sera (25-50 mul) in T4-RIA offer distinct advantages over T4(D) procedures, and in simplicity excel even other T4-RIAs. T4-RIA values in physiological and pathological states were highly correlated (r = 0.97) with T4(D) measurements and no differences between these two techniques were found. The reported discrepancies between T4-RIA and T4(D) measurements in human sera and some of the reasons for attributing these inconsistencies to probable methodological errors and variations are discussed.