At a glance

Why get tested?

To help diagnose Cushing’s syndrome or Addison’s disease or as part of a test for pituitary function or adrenal function (Synacthen test)

When to get tested?

If your doctor suspects disease of the adrenal gland or pituitary gland, or rarely a malignant tumour, that could result in the body producing too much cortisol

Sample required?

A blood sample drawn from a vein in the arm. A 24 hour urine sample or a sample of saliva may be required

Test preparation needed?

None. However samples are often taken at particular times: between 8am and 9am and/or close to midnight

What is being tested?

Cortisol is a steroid hormone, produced by the adrenal gland, in response to the pituitary hormone ACTH. Cortisol is essential for survival. It increases in times of stress and regulates the immune system. Heat, cold, infection, trauma, exercise, obesity and debilitating disease influence cortisol secretion. The hormone is secreted in a daily pattern, rising in the early morning, peaking around 8 a.m., and declining in the evening (diurnal rhythm). This pattern can change in long term night shift workers.

How is the sample collected for testing?

Typically, blood will be drawn from a vein in the arm. Sometimes urine is tested for cortisol; this requires collecting all urine produced during a day (24-hour urine). Cortisol is sometimes now measured in saliva as well. The saliva can be collected at home in special collection tubes.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

Blood, urine and saliva tests for cortisol are used to help diagnose Cushing’s syndrome and Addison’s disease, two serious disorders affecting the production of cortisol by the adrenal gland. Cushing's syndrome is caused by too much cortisol, while Addison’s disease is caused by damage to the adrenal, and is associated with too little cortisol. Drugs related to cortisol (e.g. prednisolone ) will suppress cortisol secretion from the adrenal gland if taken for a period of time. 

If cortisol is abnormal, additional testing is required to confirm the diagnosis so that you can receive treatment.

When is it requested?

A cortisol test may be requested if your doctor notices symptoms suspicious of Cushing's syndrome (high blood pressure, obesity, muscle wasting and muscle weakness) or Addison's disease (low blood pressure, weakness, fatigue, increased pigment on the skin among others), and wishes to make a diagnosis. Because of the variety of factors which influence cortisol levels, a single measurement is not usually sufficient.

If Addison's disease is suspected it may be necessary to measure the response of the adrenal glands to a stimulus such as injection of Synacthen (a synthetic form of ACTH).

If Cushing's syndrome is suspected, you may be asked to take a pill of dexamethasone (a drug that acts like cortisol and switches off ACTH secretion which is the normal stimulus for cortisol production) to make it easier to determine if you are making too much cortisol. Alternatively you may be given a tube to collect your saliva at midnight.

What does the test result mean?

Looking for reference ranges?

Adults have slightly higher cortisol levels than children. In normal people, cortisol levels are very low at bedtime, and at their highest just after waking. In Cushing's syndrome this pattern, called the diurnal rhythm, is usually lost, so bedtime cortisol or midnight salivary cortisol is often used when your doctor suspects this diagnosis.

Urine cortisol requires collecting all urine for a 24-hour period and provides information about total cortisol production by your adrenal gland. High blood and urine levels of cortisol indicate Cushing's syndrome. Low blood and urine levels, on the other hand are less useful for diagnosing Addison's disease and a stimulation test, as indicated above, is often necessary.

Is there anything else I should know?

Pregnancy, as well as physical and emotional stress, increases cortisol levels. Stress can increase your cortisol level and levels go up significantly when you are sick. Cortisol levels may also increase as a result of obesity. A number of drugs can also alter levels, particularly oral contraceptives (birth control pills), hydrocortisone (the synthetic form of cortisol) and prednisone and prednisolone.

Hypothyroidism may be associated with low cortisol levels. People taking long-term oral steroid therapy are at risk of decreasing the ability of the adrenal glands to secrete cortisol normally.

Common Questions

Do I need both tests (blood and urine), or is one better than the other?

If your doctor suspects Cushing's syndrome, both blood and urine may be tested. Blood cortisol is easier to collect but may be affected more by stress than the urine test.

How do I tell if a high cortisol level isn’t just from stress?

There are several approaches that your doctor can take. The simplest involves repeating tests at a time when you feel less stressed. Your doctor can also give you varying doses of a medicine that replaces cortisol (usually a drug called dexamethasone) to see if this decreases your cortisol level. Multiple tests are often needed to tell if stress or disease is causing a high cortisol level.