17-Hydroxyprogesterone

You don’t need to fast or avoid food before this test. 

Your doctor may ask you to have your blood taken: 

• Early in the morning (around 8am) 
• In the first half of your menstrual cycle (if you’re a woman with regular periods) 

The test uses a blood sample from a vein in your arm. For babies, a small blood sample is taken from a heel prick. 

Some specialist laboratories can also test saliva samples. 

This test measures 17-hydroxyprogesterone (17-OHP) in your blood. This is a steroid hormone your body uses to make cortisol. 

Cortisol is a vital hormone made by your adrenal glands. It helps your body: 

• Break down proteins, fats, and sugars 
• Maintain blood pressure 
• Regulate your immune system 
• Respond to stress and illness 

Your body needs two enzymes to convert 17-OHP into cortisol. If one of these enzymes is missing or not working properly, 17-OHP levels build up in your blood. Your adrenal glands then use this excess 17-OHP to make male hormones (androgens). 

The most common enzyme deficiency is called 21-hydroxylase deficiency. This accounts for about 90% of cases of congenital adrenal hyperplasia (CAH). 

If your 17-OHP is very high (newborns and infants) 

Very high levels in a newborn or infant strongly suggest severe CAH due to 21-hydroxylase deficiency. 

This severe form can cause: 

• Girls to be born with genitals that look unclear or unusual 
• Boys to develop signs of puberty much earlier than normal 
• Dangerous ​‘salt-wasting’ crises where too much salt and water is lost in urine 

If your 17-OHP is moderately raised 

• Moderately raised levels may mean: 
• A milder form of CAH (late-onset or non-classical CAH) 
• A deficiency of a different enzyme 
• A false positive result that needs follow-up testing 
• The milder form of CAH can appear at any age. Symptoms may develop slowly and vary between people. This form isn’t life-threatening but can affect growth, development, and fertility. 

If your 17-OHP is normal 

• Normal results mean you’re unlikely to have CAH due to 21-hydroxylase deficiency. 

If you’re being monitored for CAH treatment 

• Your doctor will check your 17-OHP levels regularly to see how well your treatment is working. 
• Falling or low levels mean your treatment is working well 
• Rising or high levels mean your doctor may need to adjust your medication 
• Important: Premature babies often have higher 17-OHP levels than full-term babies. If your premature baby has a raised result, the test will be repeated later.

If your newborn has high results 

Your doctor will likely request: 

• A repeat 17-OHP test to confirm the result 
• Tests for other hormones (testosterone, androstenedione, aldosterone, renin) 
• An ACTH stimulation test 
• Genetic testing to look for CYP21A2 gene mutations 
• Electrolyte tests of blood to check sodium and potassium levels 
• A karyotype test to help determine your baby’s sex 

If you’re diagnosed with CAH 

Your doctor will work with you to start treatment. This usually involves: 

• Daily medication to replace the cortisol your body cannot make (glucocorticoids)
• Sometimes medication to replace aldosterone (if your levels are low) 
• Extra medication during times of illness or stress 
• Regular monitoring tests to check your treatment is working 

You’ll need to take these medications throughout your life. 

If your results are used to investigate other conditions 

Your doctor may use this test alongside other hormone tests to: 

• Rule out CAH in women with PCOS symptoms 
• Investigate infertility
• Very rarely, investigate suspected adrenal or ovarian tumours 

Several factors can affect your 17-OHP levels: 

Higher levels can occur with: 

• Being born prematurely 
• Stress or illness 
• Taking progesterone supplements 
• Being pregnant 

The timing of your test matters: 

• Levels are highest in the morning (around 8am) 
• In women, levels vary during the menstrual cycle 
• In newborns, levels change rapidly in the first days of life 

Your doctor will take these factors into account when interpreting your results.

Your doctor may request these tests alongside or following your 17-OHP test: 

• Cortisol test – to measure your cortisol levels directly 
• ACTH test – to check the hormone that stimulates cortisol production 
• Testosterone - to measure male hormone levels 
• Androstenedione – to measure another male hormone 
• Electrolytes – to check sodium and potassium levels 
• ACTH stimulation test – to see how well your adrenal glands respond 
• Genetic testing – to identify specific gene mutations causing CAH 
• Karyotype – to determine chromosomal sex in babies with unclear genitalia 
• Urine steroid profile – to screen for rarer types of CAH 

Congenital adrenal hyperplasia (CAH) is a group of inherited conditions affecting the adrenal glands. It happens when your body cannot make enough cortisol due to missing or faulty enzymes. 

CAH can be severe or mild. Treatment involves replacing the missing hormones with daily medication. 

Learn more about congenital adrenal hyperplasia