17-hydroxyprogesterone (17-OHP)

The cut-off applies to a morning sample in the first half of the cycle; it is higher in the second half of the cycle, in pregnancy and in newborns, and labs use different cut-offs (commonly below 5 or 6 nmol/L).

17-hydroxyprogesterone is a steroid made by the adrenal glands on the way to making cortisol. If one of the enzymes on that pathway is inherited in a weaker form, 17-OHP builds up, and it is the key blood marker for the group of conditions called congenital adrenal hyperplasia. It is also made in small amounts by the ovaries.

It is requested in women with excess hair growth, acne or irregular periods to look for the milder adult form of congenital adrenal hyperplasia, in newborn screening and in children with early puberty, and to monitor treatment in people known to have the condition.

• Congenital adrenal hyperplasia, including the milder late-onset form
• The second half of the menstrual cycle and pregnancy
• Morning sampling, as it follows the cortisol rhythm
• Stress and acute illness
• Adrenal or ovarian tumours, rarely
• Premature babies, in the first weeks of life

• Steroid medicines, which switch the adrenal pathway down
• Adrenal failure
• Afternoon or evening sampling
• The combined contraceptive pill, slightly

• A sample taken in the second half of the cycle or in the afternoon can sit above the cut-off without any adrenal condition
• Stress on the day of the test raises it
• Immunoassays read higher than mass spectrometry

Best taken in the morning, before 9am, and in women during the first half of the cycle (day 2 to 5 is ideal). If the basal value is unclear a short stimulation test is done in clinic.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.