17-Hydroxyprogesterone (17-OHP) is a steroid hormone produced primarily by the adrenal glands and — in smaller amounts — by the gonads. It is an intermediate in the biosynthesis of cortisol. When the enzymes responsible for converting 17-OHP to cortisol are deficient or absent — as in congenital adrenal hyperplasia (CAH) — 17-OHP accumulates to very high levels.
CAH due to 21-hydroxylase deficiency is the most common adrenal enzyme disorder and causes elevated 17-OHP, leading to excess androgen production that can cause ambiguous genitalia in newborn girls, early puberty, acne, irregular periods, and infertility. 17-OHP is also tested to assess adrenal function and investigate unexplained androgen excess in adults.
FAQs
What is congenital adrenal hyperplasia (CAH)?
CAH is a group of autosomal recessive disorders caused by enzyme deficiencies in the cortisol synthesis pathway. The most common is 21-hydroxylase deficiency, causing 17-OHP accumulation and excess androgen production. Classic CAH can cause life-threatening adrenal crises; non-classic CAH causes androgen excess symptoms without adrenal crisis.
Can non-classic CAH be mistaken for PCOS?
Yes. Non-classic CAH can present with irregular periods, acne, hirsutism, and elevated androgens, indistinguishable from PCOS on clinical grounds. 17-OHP testing (and ACTH stimulation if borderline) distinguishes the two conditions, which have different genetic causes and management.
When should 17-OHP be tested in women?
17-OHP should ideally be tested in the early morning (8am) and in the early follicular phase (day 1-5 of the menstrual cycle), as it is highest in the early morning and rises in the luteal phase. Testing outside these windows can produce misleadingly elevated results.
Is newborn screening done for CAH in Australia?
Yes. 17-OHP is included in the routine newborn bloodspot screening programme in Australia, allowing early identification of classic CAH before adrenal crises occur. Treatment can be started promptly to prevent salt-wasting crises and manage ambiguous genitalia.
