Comparison of a fluorimetric method and a competitive protein binding assay kit for the determination of plasma...

A new competitive protein binding (C.P.B.) assay kit for the determination of plasma hydroxycorticosteroids which uses a gamma emitting isotope, selenium-75, to label the cortisol was compared with a fluorimetric method in use in a routine laboratory. The mean plasma corticosteroid level in a group of 54 normal subjects was found to be lower with the C.P.B. kit than with the fluorimetric method. The correlation coefficient between the two methods in 131 specimens from healthy subjects and patients under investigation for pituitary or adrenocortical disorders was + 0.92. The precision of the two methods was similar.