The most commonly included disorders of the endocrine system are congenital hypothyroidism (CH) and congenital adrenal hyperplasia (CAH).[11] Testing for both disorders can be done using blood samples collected on the standard newborn screening card. Screening for CH is done by measuring thyroxin (T4), thyrotropin (TSH) or a combination of both analytes. Elevated 17α-hydroxyprogesterone (17α-OHP) is the primary marker used when screening for CAH, most commonly done using enzyme-linked immunosorbant assays, with many programs using a second tier tandem mass spectrometry test to reduce the number of false positive results.[11] Careful analysis of screening results for CAH may also identify cases of congenital adrenal hypoplasia, which presents with extremely low levels of 17α-OHP.[11]