- Toshihiro Tajima: Department of Pediatrics, Jichi Children's Hospital Medical Center Tochigi, Shimotsuke, Japan.
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.