17-hydroxyprogesterone (17-OH progesterone) is a steroid hormone produced by the adrenal glands. It is an intermediary in the synthesis of cortisol. Testing for 17-hydroxyprogesterone is useful in diagnosing congenital adrenal hyperplasia (CAH), a rare genetic disorder manifested by a cortisol production deficiency that is often severe and dangerous in newborns, specifically in female fetuses, through ambiguous genital development such as clitoral hypertrophy. There are later forms of CAH with signs of virilization that appear only at puberty in young girls and that take the form of early puberty in boys. There is also an identifiable adult form in women with variable clinical manifestations, including the gradual development of signs of virilization (hirsutism), menstrual cycle abnormalities and infertility. Results are expressed in nanomoles per litre (nmol/L) and vary by sex, age (pre- or post-puberty) and stage of the menstrual cycle.
A normal result indicates that the person does not have one of the forms of congenital adrenal hyperplasia that is responsible for the signs of virilization or infertility. In prepubescent children or adult women, high levels of 17-OH progesterone indicate the probable presence of late-onset CAH.