Getting a cortisol test from your doctor: when, which test and how to prepare

A doctor will usually test your cortisol only if they suspect a condition that raises or lowers it: Cushing's syndrome, caused by too much cortisol, or adrenal insufficiency, including Addison's disease, caused by too little. They may also test people who take steroid medicines. In the UK a GP can arrange the first blood, urine or saliva tests and refer you to a hormone specialist (an endocrinologist) if the results need following up.¹² In the US your health care provider orders the tests in the same way. How you prepare matters a great deal, because cortisol moves with the time of day, with stress and exercise, and with medicines such as the contraceptive pill, HRT tablets and steroids.³⁴

When will a doctor test your cortisol?

The NHS advises seeing a GP if you have symptoms of Cushing's syndrome, particularly if you take steroid medicine, which is its most common cause.¹ The Endocrine Society recommends testing people with features that are unusual for their age, such as osteoporosis or high blood pressure, people with several features that are getting worse, and people with an adrenal lump found by chance on a scan. It recommends against widespread testing in anyone else.⁵

For low cortisol, the NHS lists extreme tiredness, weight loss, salt cravings, dizziness on standing and darker patches of skin among the symptoms of Addison's disease.² People taking steroids for a long time are a large group at risk: at least 1 per cent of the population is on long-term glucocorticoid treatment, which can stop the adrenal glands working properly.⁶ NICE advises a blood cortisol test at 8 to 9 in the morning when adrenal insufficiency is suspected.³

A doctor is unlikely to test cortisol for general stress, or for "adrenal fatigue": the Endocrine Society says there is no scientific proof that adrenal fatigue is a real condition and no test can detect it.⁷ See high cortisol symptoms, low cortisol symptoms and adrenal fatigue.

Which tests a doctor may use

For suspected Cushing's syndrome, an international consensus recommends starting with the dexamethasone test, 24-hour urine and late-night saliva, often more than one.¹⁰ If cortisol is high, the NHS says you may be referred to an endocrinologist for more blood tests and scans.¹ For suspected Addison's disease, a GP refers you to a specialist, who will usually do a Synacthen test.²⁹ Our guides to the blood, saliva and urine tests, the dexamethasone suppression test and the Synacthen test explain each in detail.

Getting a cortisol test through your GP in the UK

Book an appointment and describe your symptoms, including how long you have had them. Mention every steroid medicine you use, including inhalers, nasal sprays, creams and injections: guidelines ask doctors to take a full drug history before testing.⁵ If the GP agrees a blood test is needed, they will tell you how to book it; some surgeries and hospitals let you book online.¹¹ Ask for a morning appointment, because a random cortisol taken at another time cannot be interpreted by some laboratories.¹²

Blood test results usually come back within a few days to a few weeks. Some surgeries only contact you if they need to discuss the result, and you may be able to see it in the NHS App; if you hear nothing after a few weeks, contact the surgery.¹¹ For a morning test checking for low cortisol in adults, measured with modern laboratory methods, NICE suggests that below 150 nmol/L (about 5.4 µg/dL) means you may have adrenal insufficiency and should be referred to a specialist, 150 to 300 nmol/L is uncertain and may be repeated, and above 300 nmol/L (about 10.9 µg/dL) makes it very unlikely.³

Getting a cortisol test from a doctor in the US

Your health care provider, often a primary care doctor or an endocrinologist, orders the test. Blood is usually drawn at a laboratory, typically in the morning and sometimes again around 4 pm on the same day. Saliva may be collected at home at set times, and urine over 24 hours.⁴ Normal values for a blood sample at 8 am are 5 to 25 µg/dL (138 to 690 nmol/L), although ranges vary slightly between laboratories.¹³ For 24-hour urine, normal is below 45 µg a day for women and below 60 µg for men.¹⁴ Ask your provider and insurer about cost before the test.

How to prepare for a cortisol test

• Timing. Have a morning blood test at the time you are given, usually 8 to 9 am.³ If you work shifts, tell the doctor first: NICE guidance for GPs advises specialist advice before testing shift workers.⁹ See cortisol and shift work.
• Rest. Stress and exercise raise cortisol, so rest beforehand and avoid vigorous exercise the day before.⁴¹³ Having blood taken can itself raise cortisol in about 30 to 47 per cent of people.¹⁵
• The pill and HRT. Oestrogen taken by mouth raises the protein that carries cortisol in the blood; in one study total blood cortisol was 67 per cent higher in women taking it.¹⁶ NICE advises stopping oral oestrogen for six weeks before a blood cortisol test, and the Endocrine Society advises the same before Cushing's testing where possible.³⁵ Patches and gels did not raise total cortisol in that study.¹⁶ Only stop on the advice of the doctor arranging the test. See cortisol and the menopause.
• Steroid medicines. Inhaled, injected and skin steroids may lower a morning cortisol, and NICE advises waiting four weeks after a steroid injection into a muscle or joint before testing.³ One NHS laboratory says a cortisol taken while on steroid treatment cannot be interpreted.¹² Never stop a steroid suddenly to prepare for a test: ask first.⁴
• Saliva tests. Do not eat, drink, brush your teeth or floss for 30 minutes before collecting.⁴ Liquorice, smoking on the day and steroid creams or gels on your hands or mouth can raise a late-night saliva result.⁵

Questions to ask your doctor

• Which test is this, and what is it looking for?
• What time should the sample be taken, and does it need repeating on another day?
• Should I stop or change any medicines, including the pill, HRT, inhalers or creams, and for how long?
• How and when will I get the result?
• What range does the laboratory use? Ranges differ: one NHS laboratory gives 101 to 536 nmol/L before 10 am, another 185 to 624 nmol/L at 9 am.¹⁷¹⁸
• What happens if the result is abnormal or borderline?

What happens after the result

One result is rarely the end. A cortisol test on its own cannot show the cause of an abnormal level, so more tests usually follow. An abnormal result does not always mean a condition that needs treatment: cortisol can be temporarily high with depression, anxiety, alcohol use disorder, poorly controlled diabetes or obesity.⁴ Because high cortisol can come and go, guidelines advise at least two urine or saliva measurements when Cushing's syndrome is suspected.⁵ Adrenal insufficiency is confirmed in hospital with a Synacthen test; a peak cortisol below 500 nmol/L is diagnostic of primary adrenal insufficiency, although exact cut-offs depend on the local laboratory method.⁹

Private tests, and where hair fits

Blood, saliva and urine cortisol tests are also sold privately in the UK and the US, many of them direct to the public. The table lists tests from major providers; cortisol tests compared sets them side by side with hair.

A private result can be a useful starting point for a conversation, but if a doctor suspects a condition they may want their own tests, taken at the right time and read against a laboratory range they know.¹² Hair cortisol, which measures your average cortisol over roughly the past three months, is not part of the guidelines for diagnosing Cushing's syndrome or adrenal insufficiency, and a 2024 expert review noted it still needs validating outside research.⁵¹⁰¹⁹ It does not diagnose or rule out either condition. If your question is your long-term cortisol rather than a diagnosis, see the hair cortisol test and which cortisol test.