The specificity of enzyme immunoassays for plasma 11-deoxycortisol.

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Abstract
To develop an 11-deoxycortisol enzyme immunoassay applicable to metyrapone tests for [pituitary-adrenal reserve], the specificity obtainable with various assay systems was investigated. Four 11-deoxycortisol derivatives possessing different bridges at C-4 were covalently linked to .beta.-galactosidase to give enzyme-labeled antigens. The anti-11-deoxycortisol antisera used were those elicited in rabbits by immunization with the conjugates of these haptenic derivatives with bovine serum albumin. Enzyme immunoassays were carried out with the homologous and bridge heterologous combinations between antiserum and enzyme-labeled steroid. The specificity of these assay systems was assessed by measuring the amount of 11-deoxycortisol in human plasma specimens, and by comparison of the results with those of radioimmunoassay. The assay employing the antiserum and enzyme-labeled antigen which were prepared by the use of 4-(carboxymethylthio)-11-deoxycortisol was relatively specific. The cross-reactivities in this assay were tested with 6 kinds of closely related steroids. The selective blocking of less specific antibodies present in the antiserum was also examined. The addition of cortisol to the antiserum resulted in improvement of the specificity. The enzyme immunoassay thus developed was reasonably specific and sensitive.