A simple and rapid thyroxine radioimmunoassay (T 4-ria) in unextracted human serum; a comparison of T 4-ria and T 4 displacement assay, T 4(D), in normal and pathologic sera

Abstract

A simple, rapid and accurate thyroxine radioimmunoassay (T 4-RIA) in unextracted serum or plasma has been described, and for comparison T 4 determinations have also been made by a T 4(D) procedure using Abbott Tetrasorb kits. T 4-RIA procedure basically involved denaturation of serum to dissociate T 4-protein bond, and T 4 released was allowed to react with [ 125I]T 4-labeled T 4 antiserum elicited by immunizing rabbits against bovine thyroglobulin. The displaced unbound [ 125I] T 4 was rapidly taken up by an anionic resin sponge within 15 min and this sponge [ 125I]T 4 uptake was linearly related to T 4 present in standards or serum. The denaturation of serum effected by trichloroacetic acidsodium hydroxide permitted virtually 100% T 4 extraction recovery in normal, pregnancy, hypo- and hyperthyroid sera whereas 72.9–87.6% T 4 recovery from normal serum (and with large individual differences) was noted with lower alcohols in T 4(D) procedure. Cumbersome and/or tedious steps such as pre-extraction, centrifugation, time consuming bound and unbound hormone separation procedures, etc. are obviated in T 4-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 μ1) in T 4-RIA offer distinct advantages over T 4(D) procedures, and in simplicity excel even other T 4-RIAs. T 4-RIA values in physiological and pathological states were highly correlated ( r = 0.97) with T 4(D) measurements and no differences between these two techniques were found. The reported discrepancies between T 4-RIA and T 4(D) measurements in human sera and some