CORTISOL DIRECTLY DETERMINED IN SERUM BY FLUOROIMMUNOASSAY WITH MAGNETIZABLE SOLID-PHASE

  • 1 January 1980
    • journal article
    • research article
    • Vol. 26  (6) , 730-733
Abstract
A direct fluoroimmunoassay was developed for cortisol in serum. This method involves cortisol labeled at the 3 position with fluorescein and antibodies to cortisol coupled to magnetizable cellulose/iron oxide particles. Sodium salicylate is used as a blocking agent to prevent interference from endogenous binding proteins in serum. Serum sample and labeled cortisol are incubated with the antibody-coupled solid phase for 30 min. The solid phase is then separated and washed to remove free labeled cortisol and endogenous fluorophores of the sample. Finally the antibody-bound fraction of the labeled cortisol is eluted into an alkaline methanolic medium and its fluorescence is measured. The separation, wash and elution steps are facilitated by magnetic sedimentation. The assay is sufficiently sensitive, specific and reliable for routine use and correlates acceptably (correlation coefficient = 0.92) with an established radioimmunoassay. Precision (CV) ranged from 4-10% in experiments on 3 pooled [human] sera; analytical recovery for sera supplemented with as much as 360 .mu.g cortisol/l was 91-109%.