One step enzyme linked immunosorbent assay for direct estimation of serum cortisol

One step competitive enzyme linked immunosorbent assay (ELISA) for direct estimation of cortisol in human serum is described. Cortisol-3-O-carboxymethyloxime-bovine serum albumin (cortisol-3-O-CMO-BSA) was used as an immunogen and cortisol-21-hemisuccinate-horse radish peroxidase (cortisol-21-HS-HRP) was used as a tracer. To the cortisol antibody coated microtiter wells, standards or serum samples (25 mu l) along with cortisol-HRP conjugate(100 mu l) were incubated for 2 hours at 37 degrees C. Bound enzyme activity was measured by, using TMB/H2O2 as a substrate. In this new strategy, chilled acetone stripped pooled human serum and sodium salicylate were used for preparing the standards and blocking the cortisol binding globulin (CBG), respectively. The sensitivity of the assay was 0.28 mu g/100ml. The intraassay and interassay coefficient of variations (CVs) were ranged from 1.3% to 9.3% and 6.8% to 12.3 %, respectively. The analytical recoveries were 94% to 101.5%. The serum cortisol values, obtained by this method were correlated well with those, obtained by radioimmunoassay; r=0.95 (n=52).