Comparison of Clinical Assays for Serum Corticosteroids

Abstract

Abstract We compared results obtained by (a) chemical (spectrophotometric) and competitive protein-binding assays for serum corticosteroids, and (b) competitive proteinbinding and radioimmunoassay, with and without CCl4 extraction, for serum cortisol. The two corticosteroid methods gave identical results. Radioimmunoassay with and without a CCl4 extraction step gave identical results for cortisol. Competitive protein-binding assays for cortisol (with and without CCl4 extraction) and radioimmunoassay for cortisol gave similar results. Specimens with above-normal corticosterone or 11-deoxycortisol concentrations are an exception: only methods that included CCl4 extraction gave correct values for cortisol; methods without such an extraction step overestimated cortisol. The normal serum corticosteroid concentration (mean ± SD) was 175 ± 53 µg/liter for morning specimens, and 103 ± 40 µg/liter for specimens collected in the afternoon. For cortisol, the corresponding values were 162 ± 44 and 82 ± 29 µg/liter.