Neonatal screening for congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) is well suited for newborn screening, as it is a common and potentially fatal disease which can be easily diagnosed by a simple hormonal measurement in blood. Moreover, early recognition and treatment can prevent severe salt wasting, dehydration and death and shorten the time of male sex assignment in virilised females. In screening programmes, 17alpha-hydroxyprogesterone (17OHP) is measured in filter paper blood spots obtained by a heel puncture preferably between 2 and 4 days after birth. Three assay techniques are utilised for initial screening: radio-immunoassay (USA), enzyme-linked immunosorbent assay (Japan) and time-resolved fluoro-immunoassay (Europe). Preterm newborns have higher 17OHP concentrations in serum than babies born at term. Therefore, cut-off levels are based on gestational age (in Japan and Europe) or on birth weight (in the USA). There is a considerable variation in cut-off levels from one programme to another. This is most likely due to the different antibodies and reagents used, varying thickness and density of filter paper used for sample collection and, most significantly, the characteristics of the reference population (in terms of birth weight and gestational age). More than 30 million newborns have been screened. The prevalence of CAH in the USA and Europe is approximately 1:15000-16000, and slightly lower in Japan (1:19000). In general, severe salt wasting can be prevented, but there is a remarkable variation in the number of false-positives and false-negatives among the various programmes. Ongoing refinement of cut-oft levels is needed to improve specificity and sensitivity.