Comparison of two different radioimmunoassays to measure 17-hydroxyprogesterone during treatment monitoring of children with congenital adrenal hyperplasia due to 21-hydroxylase deficiency

BackgroundAccurate measurement of 17-hydroxyprogesterone (17-OHP) concentrations is essential for the correct diagnosis and treatment management of children with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21 OHD).MethodsWe analysed 102 serum samples from 15 children with known 21 OHD twice using two different 17-OHP assays. 17-OHP concentrations were measured by an in-house radioimmunoassay (RIA) after recovery-corrected extraction and chromatographic purification and by a commercially available RIA without extraction (Immunotech).ResultsThe correlation coefficient for results of pairs of 17-OHP concentrations was 0.974. The median ratio (17-OHP concentration measured with the commercial assay/17-OHP concentration measured with the in-house assay) was 0.593 with a 95% confidence interval ranging from 0.258 to 1.370. The ratio was constant throughout the average 17-OHP concentrations ranging from 0.24 to 149.2 nmol/L, as well as throughout the age range from 0.3 to 16.4 years.ConclusionsDespite good overall correlation, absolute 17-OHP concentrations differed dramatically. This could lead to misclassification of patients suspected for 21 OHD on the basis of the hormonal profile and to a reduced quality during treatment monitoring of patients with 21 OHD with the risk of under- and overtreatment.