What the 17-OH progesterone test shows
17-hydroxyprogesterone (17-OHP) is a steroid the adrenal glands — and, in smaller amounts, the ovaries and testes — make on the pathway that ends in cortisol; the enzyme 21-hydroxylase normally passes it to the next step. Measuring it is the standard way to screen for congenital adrenal hyperplasia (CAH), a group of inherited conditions in which that enzyme is missing or weak. MedlinePlus calls the test a check for CAH and for adrenal or ovarian androgen excess.
Its value comes from its position in the pathway. Progesterone is the raw material one step upstream; cortisol is the finished product downstream. When 21-hydroxylase cannot do its job, cortisol runs short and 17-OHP piles up behind the block — so a high 17-OHP points to that specific enzyme fault far more precisely than the general androgen markers testosterone or DHEAS, which show only that androgens are raised, not why.
17-OH progesterone normal range
17-OHP is reported in ng/dL in the United States and in nmol/L (SI units) elsewhere, and the two are not equal: multiply ng/dL by about 0.03 to get nmol/L (1 nmol/L ≈ 33 ng/dL). Typical early-morning adult orientation values:
| Group | Orientation, ng/dL (nmol/L) |
|---|---|
| Men (adult) | < ~220 (< ~6.6) |
| Women, follicular phase | < ~80 (< ~2.4) |
| Women, luteal phase | < ~285 (< ~8.6) |
| Women, postmenopausal | < ~50 (< ~1.5) |
| Children, prepubertal | < ~100 (< ~3) |
| Newborns | higher — screening uses birth-weight and gestational-age cutoffs |
Two thresholds matter more than the “normal” band. An early-morning, follicular-phase baseline below 200 ng/dL (about 6 nmol/L) makes non-classic CAH unlikely, while a value at or above it prompts a stimulation test, per the Endocrine Society guideline. A stimulated 17-OHP above 1,000 ng/dL (about 30 nmol/L) then confirms 21-hydroxylase deficiency; classic CAH usually reads in the thousands. Ranges depend on the lab, assay, sex, age and cycle phase — read your result against your own report.
Why 17-OH progesterone is high
A raised 17-OHP is the usual reason for the test. Causes run from common and mild to rare and urgent:
- Non-classic (late-onset) CAH — the commonest cause of a mildly-to-moderately raised value in teens and adults. This partial 21-hydroxylase deficiency shows up as androgen excess — acne, unwanted hair growth (hirsutism), irregular periods, reduced fertility — and overlaps heavily with PCOS.
- Classic CAH — a severe, near-complete enzyme block found on newborn screening or in infancy, with a markedly high 17-OHP. Its salt-wasting form can cause a life-threatening adrenal crisis in the first weeks of life. 21-hydroxylase deficiency accounts for about 95% of all CAH.
- Sample timing — the luteal phase, pregnancy and afternoon draws all raise 17-OHP, and stress or illness pushes it up through ACTH. A high value taken in the wrong window often normalizes on a properly timed repeat.
- Other causes — 11β-hydroxylase deficiency (the second commonest CAH form) and, rarely, a steroid-producing adrenal or ovarian tumor.
When is it urgent? A newborn with a high screen plus vomiting, poor feeding, dehydration or lethargy may be in a salt-wasting adrenal crisis — a medical emergency needing same-day care.
Why 17-OH progesterone is low
A low 17-OHP is rarely a problem in itself — the high side carries the clinical weight — but a low or suppressed value shows up in a few settings:
- Glucocorticoid treatment — steroid medication (including CAH treatment itself) suppresses adrenal output; a lower result is actually the goal when monitoring treated CAH.
- Adrenal insufficiency — Addison’s disease or an underactive pituitary lower all adrenal steroids, though cortisol and ACTH are the primary tests.
- 17α-hydroxylase deficiency — a rare fault one step earlier, so 17-OHP cannot be made; it causes high blood pressure with low potassium.
- Hormonal contraception — combined pills can lower a woman’s 17-OHP.
What to test alongside
17-OHP is read next to the hormones on its pathway and the markers that sort out androgen excess:
- Progesterone — the immediate precursor; also confirms cycle phase.
- Cortisol — the end-product that runs short in CAH.
- DHEAS — an adrenal androgen that points to an adrenal source.
- Testosterone and free testosterone — quantify the androgen excess behind hirsutism or virilization.
- SHBG — the carrier protein that sets how much testosterone is active.
- LH and FSH — map the ovarian axis and help separate CAH from PCOS.
- Prolactin — routine in the work-up for irregular periods.
- AMH — often raised in PCOS, the main look-alike.
- TSH — a routine check when periods are irregular.
- Glucose — screens for the insulin resistance that travels with PCOS.
What to do about an abnormal result
- Don’t self-treat. Do not start, stop or adjust any steroid on your own; 17-OHP is a diagnostic clue, not a treatment target.
- Repeat with correct timing. Recheck a borderline value on an early-morning sample, in the first few days of the cycle (follicular phase) for menstruating women; many settle on a properly timed repeat.
- Confirm with a stimulation test. If the baseline stays at or above about 200 ng/dL (6 nmol/L), an endocrinologist arranges an ACTH (cosyntropin) stimulation test; a stimulated value above roughly 1,000 ng/dL (30 nmol/L) confirms 21-hydroxylase deficiency. Genetic (CYP21A2) testing can confirm it and inform family planning.
- Treat a newborn screen as time-critical. A positive newborn result needs prompt pediatric-endocrine assessment, and signs of a salt-wasting crisis are an emergency.
- See the right doctor. Primary care or gynecology usually orders the first test; endocrinology confirms and manages CAH, with genetic counseling for confirmed cases.
Mini-FAQ
What does a high 17-OH progesterone mean?
Most often non-classic congenital adrenal hyperplasia — a mild inherited enzyme block that raises adrenal androgens. A very high level in a newborn signals the classic, severe form, and a luteal-phase or afternoon sample can read falsely high.
How is 17-OH progesterone different from progesterone and cortisol?
It sits between them in the adrenal pathway — made from progesterone and normally turned into cortisol. When 21-hydroxylase is missing, cortisol falls and 17-OH progesterone builds up, which is what flags congenital adrenal hyperplasia.
When should 17-OH progesterone be measured?
In the early morning, and for women who menstruate in the first few days of the cycle (follicular phase). Luteal-phase and afternoon samples are naturally higher and can look falsely abnormal.
What is the ACTH stimulation test for?
A borderline-high baseline result is confirmed with an ACTH (cosyntropin) stimulation test. A stimulated 17-OH progesterone above about 1,000 ng/dL (30 nmol/L) confirms 21-hydroxylase deficiency.
Can 17-OH progesterone tell congenital adrenal hyperplasia apart from PCOS?
Yes — that is a main reason it is ordered. Non-classic CAH and PCOS look alike (acne, extra hair, irregular periods), but a raised 17-OH progesterone points to CAH, so it is checked before settling on PCOS.
