Cortisol

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

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.

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.

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 hyperthyroidism or obesity. A number of drugs can also alter levels, particularly oral contraceptives (birth control pills), hydrocortisone (the synthetic form of cortisol) and predisone and prednisolone.

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