Comparison of clinical assays for serum corticosteroids.

We compared results obtained by (a) chemical (spectrophotometric) and competitive protein-binding assays for serum corticosteroids, and (b) competitive protein-binding and radioimmunoassay, with and without CCI-4 extraction, for serum cortisol. The two corticosteroid methods gave identical results. Radioimmunoassay with and without a CCI-4 extraction step gave identical results for cortisol. Competitive protein-binding assays for cortisol (with and without CCI-4 extraction) and radioimmunoassay for cortisol gave similar results. Specimens with above-normal corticosterone or 11-deoxycortisol concentrations are an exception: only methods that included CCI-4 extraction gave correct values for cortisol; methods without such an extraction step overestimated cortisol. The normal serum corticosteroid concentration (mean plus or minus SD) was 175 plus or minus 53 mug/liter for morning specimens, and 103 plus or minus 40 mug/liter for specimens collected in the afternoon. For cortisol, the corresponding values were 162 plus or minus 44 and 82 plus or minus 29 mug/liter.