Development of a direct fluoroimmunoassay for serum levels of 17-hydroxyprogesterone.

A direct, rapid and highly specific fluoroimmunoassay for determining serum levels of 17-hydroxyprogesterone has been developed. It is based on the use of a sheep antiserum covalently coupled to magnetisable particles and fluorescein-labelled steroid. Sodium salicylate is employed to eliminate interference from endogenous binding proteins in serum. The sensitivity of 0.5 nmol/L is adequate for clinical purposes. Analytical recovery, linearity and precision are satisfactory and the results obtained correlate closely with those of an established radioimmuno-assay using 3H-labelled steroid and the same antiserum after initial sample extraction and chromatography. The values found for serum from normal adult subjects ranged from 1.0 to 12.6 nmol/L while those from treated and untreated patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency were 1.5 to 19.0 and 28.0 to 655 nmol/L, respectively.