Single-Antibody Technique for Radioimmunoassay of Cortisol in Unextracted Serum or Plasma

Abstract A radioimmunoassay procedure for cortisol is described that requires only 5 µl of serum or plasma. Native cortisol-binding proteins are denatured by heating 5 µl of sample in 0.2 ml of glutamate buffer in a boiling water bath for 15 min. After a 2-h incubation of heat-treated serum or plasma with H3cortisol and cortisol antibody, "free" and "bound" cortisol are separated by use of hemoglobin-coated charcoal. The method is easy and sensitive, and results compare favorably with those of a well-accepted acid-fluorescence method. In addition, we show that serum and heparinized plasma yield the same results by this method, and therefore either can be assayed by this procedure.