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Cutoff Levels of 17--Hydroxyprogesterone in Neonatal Screening for Congenital Adrenal Hyperplasia Should Be Based on Gestational Age Rather Than on Birth Weight

Department of Pediatrics (H.J.v.d.K., J.M.W.), Leiden University Medical Center, 2300 RC Leiden, The Netherlands; Organization for Applied Scientific Research (TNO) Prevention and Health (C.G.M.O., P.H.V.), 2301 CE Leiden, The Netherlands; Diagnostic Laboratory for Infectious Diseases and Perinatal Screening (B.H.E.), National Institute of Public Health and the Environment (RIVM), 3720 BA Bilthoven, The Netherlands; General Clinical Laboratory (M.v.B.), IJsselland Hospital, 2900 AR Capelle a/d IJssel, The Netherlands; and Department of Pediatric Endocrinology (B.J.O.), University Medical Center St. Radboud, 6500 HB Nijmegen, The Netherlands

Address all correspondence and requests for reprints to: H. J. van der Kamp, Department of Pediatrics, H-3Q, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands. E-mail: H.J.van_der_Kamp{at}LUMC.nl.

Objective: In newborn screening programs for congenital adrenal hyperplasia, 17--hydroxyprogesterone (17OHP) cutoff levels are based on birth weight (BW) or on gestational age (GA). We investigated which approach would result in the greatest specificity and sensitivity.

Study design: For the determination of 17OHP, a neonatal 17OHP assay was used in filter paper blood of 9492 newborns. The relationships between 17OHP and BW and between 17OHP and GA were studied by regression analysis. Reference curves with a specificity of 99.95% were constructed with the method that summarizes the distribution by three smoothed curves representing the skewness (L curve), the median (M curve), and the coefficient of variation (S curve). Median cutoff levels for BW and for GA according to the 99.95% reference curves were calculated.

Results: Regression analysis showed that GA is a better predictor of 17OHP than BW (R² was 50.6 vs. 35.8%, respectively). At a specificity of 99.95%, the calculated median 17OHP cutoff level was lower for GA [12.6 µg/liter (38 nmol/liter)] than for BW [17.6 µg/liter (54 nmol/liter)], thus leading to a greater sensitivity.

Conclusion: This study demonstrates that GA is a better predictor of 17OHP in newborns and will result in greater specificity than BW despite the fact that the determination of GA might be less reliable than BW.

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