Neonatal Screening for 21-Hydroxylase Deficient Congenital Adrenal Hyperplasia—The Role ofCYP21Analysis

Neonatal screening for 21-hydroxylase deficient congenital adrenal hyperplasia (21OH-CAH), an autosomal recessive disorder with an incidence of approximately 1 in 15,000 live births in North America, became feasible in 1977 with the development of a microfilter paper radioimmunoassay for measurement of capillary blood concentrations of 17-hydroxyprogesterone (17OHP) by Pang et al. (1). Subsequently, the method has been modified by the use of polyclonal and monoclonal antibodies with differing specificities for 17OHP in single or dual antibody sandwich assays and the use of either radioactive, enzymatic, or fluorometric markers of antibody-antigen interaction. The immunological measurement of 17OHP in neonatal whole blood is relatively nonspecific because the fetal adrenal cortex secretes a large number of compounds that are immunologically similar to and cross-react in immunoassays for 17OHP (2, 3). In addition to the problem of assay specificity, circulating levels of 17OHP decline with gestational maturity and fall rapidly after birth (4). Thus, normal whole blood screening values of 17OHP must be determined for neonates of varying birth weight and gestational duration as well as for postnatal age (5).