Neonatal Screening for CAH in Sweden—Results of Implementing Second-Tier Testing

Newborn screening for congenital adrenal hyperplasia (CAH) is effective in identifying patients with severe forms before a potentially lethal crisis, but has a relatively high false-positive rate. The aim of this study was to improve the national neonatal screening program in Sweden and the positive predictive value by implementing LC-MS/MS second-tier testing. A combination of two independent parameters, the steroid hormone ratio (androstenedione+17-hydroxyprogesterone)/cortisol and the concentration of 21-deoxycortisol and adjustment of cut-off levels resulted in an increase in the positive predictive value (PPV) from 14% to 84% for full-term infants. In total, the false-positive screening cases decreased by 88%. CYP21A2 genotyping was used to determine the severity of CAH in identified cases. We report on the stepwise approach that was used to optimize the cut-off levels for full-term and preterm infants in order not to miss any true cases in the process.