Nonspecificity of a direct 17 alpha-hydroxyprogesterone radioimmunoassay kit when used with samples from neonates

We analyzed 240 samples for 17 alpha-hydroxyprogesterone (17-OHP) with the direct-assay kit ("Coat-A-Count" method for serum samples) from Diagnostic Products Corp. (DPC). The specimens were from 50 patients with known or suspected congenital adrenal hyperplasia (CAH); 74 mostly hospitalized neonates and infants, ages three days to three months; and 116 other patients, ages six months to 23 years. Samples from the CAH group were also analyzed with our in-house assay. For 39 of the neonatal samples, the analysis with the DPC assay was repeated with re-solubilized material that had been extracted from the serum with organic solvents. Values for "17-OHP" measured with the DPC direct assay were high, not only in CAH patients, but also in many of the unaffected neonates and infants. The extraction properties of the cross-reacting immunoreactive material into various organic solvent systems were different from those of 17-OHP, and were more like those of steroid sulfates. Because of this significant cross-reactivity, we recommend that the DPC kit not be used for sera from children younger than six months of age, unless the method is modified to include an extraction step.