A solid phase fluoroimmunoassay of serum cortisol.

Direct solid phase fluoroimmunoassay of serum cortisol was established by using fluorescein isothiocyanate labelled anti-cortisol antibody and cortisol conjugated polyacrylamide beads. Sodium salicylate was used as a blocking agent for cortisol binding proteins. The sensitivity of this assay was 0.2 ng/assay tube and the measurable range was from 2 to 100 micrograms/dl using 10 microliters of serum. Intra- and inter-assay coefficients of variation were 11.6% (mean +/- SD 19.8 +/- 2.3 micrograms/dl, n = 5): and 12.1% (mean +/- SD 22.8 +/- 2.8 micrograms/dl, n = 5), respectively. THe accuracy was estimated from recovery study and the average recovery was 100.2%. Cortisol values determined by the present method correlated well with those determined by radioimmunoassay (r = 0.98, y = 0.98 x + 0.04, n = 35). The proposed assay satisfied the standard criteria of dilution, accuracy, and precision, and is applicable to routine measurement of serum cortisol.