Serum 17α-hydroxyprogesterone in infants and children as measured by a direct radioimmunoassay kit

Abstract

A direct 17 alpha-hydroxyprogesterone (17-OHP) radioimmunoassay kit was used for the assay of samples from 219 infants and children. The kit was used according to the manufacturer's protocol on unextracted serum or plasma and also on reconstituted material extracted from the serum with propanol-heptane. The extraction protocol recovers approximately 88% of 17-OHP. Patients were grouped as infants 3-90 days (96 subjects) or older children, adolescents and young adults 91 days-20 years (123 subjects). 17-OHP results by the direct and extraction protocols correlated but the slopes of the regression lines (0.43 and 0.63) differed in the two groups, indicating that only about 49% of the immunoreactive material measured by the kit in the infants was 17-OHP whereas the corresponding percentage was 72% in the older children. Despite this nonspecificity, the present antibody is much more specific for 17-OHP in the presence of neonatal plasma steroids than that used previously. Reference values were obtained for the two groups using the method with and without an extraction step. 17-OHP values on four untreated patients with CAH were clearly elevated at the time of diagnosis. It is recommended that when the kit is used with neonatal and infant samples, an extraction step should be incorporated to enhance specificity.