Simultaneous measurement of free triiodothyronine and free thyroxine by equilibrium dialysis and immunoassay

摘要

The present invention provides methods for the simultaneous measurement of triiodothyronine (T.sub.3) and thyroxine (T.sub.4) in biological fluids such as serum by direct equilibrium dialysis and immunoassay. Specifically, the method comprises dialyzing the serum sample to equilibrium in a physiological buffer system so that the free T. sub.3 and the free T.sub.4 are separated from T.sub.3 and T.sub.4 bound to serum proteins. The method further comprises combining a measured quantity of the dialyzed serum sample having free T.sub.3 and free T.sub. 4 with reagents comprising a measured quantity of T.sub.3 labelled with a detectable marker and a measured quantity of T.sub.4 labelled with a detectable marker; an anti-T.sub.3 antibody of sufficient specificity and in sufficient quantity to bind a measurable quantity of the free T.sub.3, and an anti-T.sub.4 antibody of sufficient specificity and in sufficient quantity to bind a measurable quantity of the free T.sub.4. The method then comprises allowing reaction of the free T.sub.3 and the free T.sub.4 and the labelled T.sub.3 and the labelled T.sub.4, with the anti-T.sub.3 antibody and the anti-T.sub.4 antibody to proceed substantially to equilibrium to thereby produce antibody bound labelled T.sub.3 and antibody bound labelled T.sub.4. Finally, the method comprises separating the unbound labelled T.sub.3 from the antibody bound labelled T.sub.3 and the unbound labelled T.sub. 4 from the antibody bound labelled T.sub.4 ; and determining the levels of T.sub.3 and T.sub.4 in the sample by comparing relative amounts of antibody bound labelled T.sub.3 and T.sub.4 and unbound labelled T.sub.3 and T.sub.4. In one embodiment of this method, the assay is a radioimmunoassay.