Blood test
Cortisol Test
A cortisol test measures the level of the stress hormone cortisol, made by the adrenal glands. It helps diagnose conditions where cortisol is too high or too low.
Quick answer
Cortisol Test: what it is and what the results mean
Cortisol is a hormone made by the adrenal glands that helps the body respond to stress and regulate metabolism. A cortisol test measures its level in blood, and sometimes in saliva or urine.
- Why it is done: It is used to investigate conditions where cortisol is too high (such as Cushing’s syndrome) or too low (such as Addison’s disease), and to assess symptoms like unexplained tiredness, weight change or low blood pressure.
- Understanding results: A very high or very low level, or an abnormal response to a stimulation or suppression test, can point to an adrenal or pituitary problem.
What it is
Cortisol is a hormone made by the adrenal glands that helps the body respond to stress and regulate metabolism. A cortisol test measures its level in blood, and sometimes in saliva or urine.
Why it is done
It is used to investigate conditions where cortisol is too high (such as Cushing’s syndrome) or too low (such as Addison’s disease), and to assess symptoms like unexplained tiredness, weight change or low blood pressure.
What to expect
Because cortisol varies through the day, timing matters — blood is often taken in the morning. Some assessments use special tests, such as measuring cortisol after a medicine, or samples of saliva or 24-hour urine.
Understanding the results
A very high or very low level, or an abnormal response to a stimulation or suppression test, can point to an adrenal or pituitary problem. Results are interpreted with the timing, the type of test and your symptoms.
Good to know
Risks and limitations
The blood test is very safe. Because cortisol naturally rises and falls and is affected by stress and illness, careful timing and sometimes specialised tests are needed for a reliable answer.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Cortisol Test: frequently asked questions
Why is a cortisol test done in the morning?
Cortisol is usually highest in the morning and lowest at night, so morning timing gives a meaningful baseline. Some conditions are assessed with special tests at particular times or after a medicine.
What does low cortisol mean?
Low cortisol can suggest the adrenal glands are underactive, as in Addison’s disease, which needs treatment. Results are confirmed with further tests and interpreted alongside your symptoms.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Association for Laboratory Medicine / relevant professional body
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