Abstract
In Japan, newborn screening (NBS) for congenital adrenal hyperplasia (CAH) began in 1989. NBS is useful for early diagnosis and preventing gender misidentification, however, it has a higher false positive rate for CAH compared to other diseases detected by neonatal screening. Recently, it has become clear that using liquid chromatography with tandem mass spectrometry (LC-MS/MS) for second-tier testing reduces false positive rates and repeat blood sampling. LC-MS/MS commonly measures cortisol (F), androstenedione (A4), 11-deoxycortsiol (11DOF), 21-deoxycortisol (21DOF), and 17-hydroxyprogesterone (17OHP) levels. The ratios for (21DOF+17OHP)/F and (17OHP+A4)/F have been used to establish cut-off values for the second-tier test. In Japan, the recall rate is reduced using the 11DOF/17OHP ratio as well as the ratios for (21DOF+17OHP)/F and (17OHP+A4)/F for the second-tier test. Currently, second-tier testing using LC-MS/MS for CAH neonatal screening is unfeasible in all regions of Japan due to equipment costs, however, it will hopefully be available nationwide in the future.