The specificity in enzyme immunoassay for plasma and urine cortisol.

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Abstract
The specificity in heterogeneous enzyme immunoassays for cortisol was investigated. Enzyme labeling of cortisol was accomplished by the N-succinimidyl ester method at an appropriate molar ratio of steroid to enzyme. Three cortisol derivatives possessing different bridges at C-4 were covalently linked to .beta.-galactosidase. The anticortisol antisera used were those elicited in rabbits by immunization with the conjugates of these haptenic derivatives with bovine serum albumin. With the aim of obtaining high sensitivity, enzyme immunoassays were carried out in the bridge heterologous combinations of antiserum and enzyme-labeled cortisol. The specificity of these assay systems was assessed by measuring the amount of cortisol in biological fluids, and by comparison of the results with those of radioimmunoassays. The cross-reactivities were also tested with 15 closely related steroids. The assay using the antiserum raised against the 4-(2-carboxyethylthio)cortisol-protein conjugate was relatively specific and applicable to the determination of cortisol in human plasma and urine.

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