Direct solid-phase radioimmunoassay for screening 17 alpha-hydroxyprogesterone in whole-blood samples from newborns

We describe a direct, solid-phase RIA for 17 alpha-hydroxyprogesterone (17-OH-P) that we are using to screen neonates for congenital adrenal hyperplasia. Phosphate buffer containing danazol and anti-17-OH-P is placed in tubes coated with antibody to IgG. The tubes also contain standards, controls, or blood samples on filter paper discs 3 mm in diameter. 125I-labeled 17-OH-P is added to each tube. The mixture is vortex-mixed and incubated overnight. The fluid and disc are removed, the radioactivity remaining in the tubes is counted, and the amount of 17-OH-P per disc is calculated by using a log-logit transformation of the standard curve. Results compare favorably with those by two extraction assays. Inter- and intra-assay CVs were less than 11% and less than 9%, respectively. Sensitivity was 2 pg per assay tube. There is no significant cross reactivity with structurally related steroids at their physiological concentrations. Analytical recovery of added 17-OH-P averaged 104%. 17-OH-P in whole blood spotted on filter paper is stable for at least six months.