Cortisol is a hormone that is essential to many of the body's vital processes. It helps to control metabolism, fight infection, regulate blood glucose, and maintain blood pressure. It also has an important role to play in priming the body to respond to stress. Cortisol is produced by the adrenal glands which sit on top of the kidneys. Levels are regulated by the hypothalamus in the brain and the pituitary gland. Too much cortisol can lead to the condition known as Cushing's syndrome while insufficient cortisol causes the condition Addison's disease. These disorders of the pituitary and adrenal glands can be diagnosed by measuring levels of cortisol in the blood, urine and/or saliva.

Cortisol is a steroid hormone that is produced by the adrenal glands which sit on top of your kidneys.  Heat, cold, infection, trauma, exercise, obesity and debilitating disease influence the amount of cortisol being released. Cortisol levels follow a daily pattern, rising in the early morning, peaking at about 8 a.m., and falling in the evening. This is known as the diurnal rhythm. The pattern can change in long-term night-shift workers.

Production of cortisol is controlled by the hypothalamus, a region at the base of the brain, and the pituitary gland which is located just below the brain. When levels of cortisol fall the hypothalamus sends signals to the pituitary to produce ACTH (adrenocorticotropic hormone) which stimulates the adrenal glands to produce more cortisol.

In order for the correct amounts of cortisol to be made and secreted into the bloodstream the hypothalamus, the pituitary and the adrenal glands must all be functioning properly.

Blood, urine and saliva tests can be used to measure cortisol. A cortisol test is most often ordered to diagnose:

• Cushing's syndrome (high cortisol, high blood pressure, obesity, muscle wasting and muscle weakness) or 
• Addison's disease (low cortisol, low blood pressure, weakness, fatigue, increased pigment on the skin among others). 

Because of the variety of factors that influence cortisol levels a single measurement is not usually enough. If your cortisol levels are not within the normal range additional testing is usually required to confirm the diagnosis before you can have the appropriate treatment.

Ways of testing

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

Addison's disease:  To diagnose Addison's disease only blood cortisol is needed but it is likely that samples before and after a Synacthen injection (synthetic ACTH) will be needed to test the functioning of the adrenal glands.

Sample

Blood, urine and saliva.

Any preparation?
None.

Reading your test report

Your results will be presented along with those of your other tests on the same form.  You will see separate columns or lines for each of these tests.  

In healthy people blood and saliva cortisol levels are very low at midnight and at their highest just after waking.  Adults have slightly higher morning cortisol levels than children. 

In Cushing's syndrome this pattern, called the diurnal rhythm, is usually lost, so late night blood or saliva 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 glands over the whole day. High late-night blood and saliva cortisol and high 24-hour urine cortisol results suggest Cushing's syndrome.

If you are being tested for Cushing's syndrome and your doctor wants to make sure that your high levels of cortisol are not just the result of your body being stressed, you may be asked to take a dexamethasone pill the night before having a cortisol test.  The dexamethasone pill acts like cortisol and switches off ACTH production. It helps differentiate between Cushing's syndrome and stress.  Otherwise, you may be given a tube to collect your saliva late at night or asked to collect a 24-hour urine sample for cortisol measurement.

Low morning blood cortisol does not necessarily mean Addison's disease and a Synacthen stimulation test (synthetic ACTH) is often needed.

Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people. 
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor. 

The choice of tests your doctor makes will be based on your medical history and symptoms.   It is important that you tell them everything you think might help. 

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely. 

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

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.

People taking long-term oral steroid therapy are at risk of decreasing the ability of the adrenal glands to secrete cortisol normally.

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

Get further trustworthy health information and advice from healthdirect.