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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.
Foster et al. (Fri,) studied this question.