A sensitive enzyme immunoassay for plasma cortisol.

A sensitive enzyme immunoassay for plasma cortisol has been developed, using cortisol-beta-D-galactosidase conjugate as labelled antigen and 4-methylumbelliferyl-beta-D-galactoside as fluorescence substrate. Sensitivity and precision were compared with those of radioimmunoassay with 3H-labelled cortisol and the same antiserum. The minimal detectable level for the enzyme immunoassay was 10 pg/tube or 1 microgram/dl of plasma, which makes it slightly more sensitive than the radioimmunoassay and 10 times more sensitive than previously reported enzyme immunoassays. However, the precision of the enzyme immunoassay was inferior to that of the radioimmunoassay.