Radioimmunoassay of thyroxine in unextracted serum, by a single-antibody technique.

A radioimmunoassay procedure for thyroxine (14) is described, for which only 25 il of serum is required. The antibody, commercially available, is produced in rabbits in response to injections of a T4-albumin conjugate. Native T4-binding proteins are denatured by heating 25 .tl of serum in 0.2 ml of a glutamate buffer in a boiling water bath. After a 1-h incubation of heat-treated serum with l125T4 and 14 antibody, “free” and “bound” 14 are separated by use of hemoglobin-coated charcoal. The method has excellent sensitivity, is rapid, and possesses significant advantages over a standard competitive protein binding method with which it is compared.