Introduction: Screening for congenital adrenal hyperplasia (CAH) by measurement of 17-hydroxyprogesterone (17-OHP) in dried blood spots results in a high false positive rate among preterm newborns admitted in a neonatal intensive care unit (NICU). We searched for risk factors of this population for raised 17-OHP levels.
Methods: We retrospectively collected clinical characteristics (prenatal, at birth, postnatal) in newborns with an increased 17-OHP level at initial screening (> 30 nmol/L for a birth weight > 2000 g and > or = 60 nmol/L for a birth weight < or = 2000 g), that turned out to be false positive (no CAH). The correlation of these characteristics with individual 17-OHP levels was evaluated. We also performed a case-control study matched for gestational age (GA).
Results: In 94 screened newborns 17-OHP levels were raised at initial screening. Negative correlations were found between 17-OHP levels and GA and birth weight, positive correlations with prenatal betamethasone administration and several parameters of respiratory disease. In a multiple regression model GA was the dominant variable. In the case control study with 91 index patients admitted to the NICU (91/1275 newborns admitted to the NICU, 7.1%) a positive correlation with respiratory disease was confirmed and cases had a significant higher birth weight and a significant lower incidence of prenatal betamethasone administration. Application of new cutoff tables adjusted by GA and/or day of sampling would have resulted in a reduction in false positive rate.
Conclusion: The dominant risk factor for a false positive screening during NICU admission is GA. Prenatal administration of betamethasone and birth weight are more complex risk factors. These observations support the use of new cut-off values based on GA to reduce the problem of false positive screening.