Screening for congenital adrenal hyperplasia: adjustment of 17-hydroxyprogesterone cut-off values to both age and birth weight markedly improves the predictive value.

Newborn screening procedures for congenital adrenal hyperplasia (CAH) are still suboptimal because of low specificity, particularly in premature infants. This study evaluated a multitiered strategy for reporting abnormal 17-hydroxyprogesterone screening values that simultaneously takes into account not only birth weight but also age at sampling. A cautious three-tiered cut-off scheme was used during the initial 24 months of CAH screening in Bavaria. Data were then reanalyzed using five birth weight classes to reflect more precisely the markedly higher values in low-birth-weight newborns. Because 17-hydroxyprogesterone values apparently decline with increasing age, these classes were then further subdivided into a total of 21 groups according to the age at sampling. Based on this reanalysis, we defined new multitiered cut-off levels and used them for the next 18 months. A total of 538466 newborns were screened from January 1999 to June 2002; 51 CAH cases were detected. Application of the new threshold values resulted in a 35% reduction of the total recall rate (from 1.13% to 0.74%) and an increase in the positive predictive value from 0.84% to 1.29% without reducing diagnostic sensitivity. This improvement of CAH screening can be achieved by simply using request forms that ask for both age and birth weight at the time of sampling.