17-Hydroxyprogesterone (17-OHP)
17-hydroxyprogesterone is a steroid intermediate in the cortisol synthesis pathway. When 21-hydroxylase enzyme is deficient — the most common cause of congenital adrenal hyperplasia (CAH) — 17-OHP accumulates. 17-OHP is the primary biochemical marker for classical (neonatal) and non-classical (late-onset) CAH. Non-classical CAH presents in adolescent or adult women with hirsutism, acne, and irregular periods and can be mistaken for PCOS.
Reference Ranges
Male
0 – 2
ng/mL
Female
0 – 2
ng/mL
Child
0 – 1
ng/mL
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low 17-OHP is normal and reassuring — it rules out CAH in most clinical settings. In adrenal insufficiency, 17-OHP can be low along with cortisol, but ACTH stimulation testing rather than 17-OHP alone is used to diagnose adrenal insufficiency.
What High Levels Mean
17-OHP above 2 ng/mL in the follicular phase is abnormal in adult women. Above 10 ng/mL strongly suggests classical CAH; between 2–10 ng/mL warrants ACTH stimulation testing to differentiate non-classical CAH from PCOS. In newborns, elevated 17-OHP on heel-prick screening prompts urgent confirmatory testing — classical CAH can cause life-threatening salt-wasting crisis in the first weeks of life.
Frequently Asked Questions
Why is 17-OHP measured in PCOS workup?
To rule out non-classical CAH, which clinically resembles PCOS (hirsutism, acne, irregular cycles). Around 1–5% of women diagnosed with PCOS actually have non-classical CAH. Basal 17-OHP above 2 ng/mL in the follicular phase warrants ACTH stimulation testing. The distinction matters because treatment differs — hydrocortisone suppresses androgen output in CAH, whereas PCOS is managed differently.
How should 17-OHP be collected?
Early morning (before 10 AM), in the follicular phase for menstruating women. ACTH is highest in the morning and drives 17-OHP, so afternoon samples are less useful. In women with irregular cycles, early follicular sampling may not be feasible — in that case, ACTH stimulation testing is preferred over basal sampling.
Why is newborn screening for 17-OHP done?
Classical CAH (21-hydroxylase deficiency) causes severe salt-wasting crisis and virilization of female newborns. Early detection via heel-prick 17-OHP screening (typically day 2–5 of life) allows prompt treatment with hydrocortisone and fludrocortisone, preventing crisis and ambiguous genitalia surgical decisions. Universal newborn screening is standard in many Indian states and increasingly recommended nationally.
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nmol/LThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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