Enzyme immunoassay for plasma 11-deoxycortisol. Application to metyrapone test.

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Abstract
A sensitive and relatively specific enzyme immunoassay of 11-deoxycortisol in human plasma was developed. Enzyme labeling of 11-deoxycortisol was accomplished by the active ester method. The use of 4-carboxymethylthio-11-deoxycortisol N-succinimidyl ester and .beta.-galactosidase in an appropriate molar ratio provided an enzyme-labeled antigen suitable for enzyme immunoassay. The anti-11-deoxycortisol antiserum used was that elicted in the rabbit by immunization with the conjugate of the haptenic derivative with bovine serum albumin. In order to improve the assay specificity, cortisol was used as an agent for the blocking of less specific antibodies present in the antiserum. The specificity of the assay system was assessed by comparing the results of measurement of 11-deoxycortisol in human plasma with those obtained by a radioimmunoassay. The quantitation limit of 11-deoxycortisol was 800 fg/tube. The intra- and inter-assay coefficients of variation for 11-deoxycortisol in human plasma were 3.0-15.8% and 7.6-12.5%, respectively. The present enzyme immunoassay of 11-deoxycortisol was useful in the metyrapone tests for evaluation of pituitary-adrenal function and for differential diagnosis of Cushing''s syndrome. The assay can be done on methylene chloride extracts of plasma.