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A cortisol level is a blood test that measures the amount of cortisol, a steroid hormone produced by the adrenal gland.

Serum cortisol

A blood sample is needed. For information on how this is done, see: Venipuncture

Usually, the health care provider will ask that the test be done in the morning. This is important, because cortisol levels vary throughout the day.

The health care provider may ask you to stop taking drugs that can affect the test. Drugs that can increase cortisol measurements include:

• Estrogen
• Human-made (synthetic) glucocorticoids, such as prednisone and prednisolone

Drugs that can decrease cortisol measurements include:

• Androgens
• Phenytoin

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

The test is done to check for increased or decreased cortisol production. Cortisol is a steroid hormone released from the adrenal gland in response to ACTH, a hormone from the pituitary gland in the brain.

Cortisol affects many different body systems. It plays a role in:

• Bone
• Circulatory system
• Immune system
• Metabolism of fats, carbohydrates, and protein
• Nervous system
• Stress responses

Different diseases, such as Cushing's disease and Addison's disease, can lead to either too much or too little production of cortisol. Cortisol levels are often measured to help diagnose these conditions and to evaluate how well the pituitary and adrenal glands are working.

Normal values for a blood sample taken at 8 in the morning are 6 - 23 micrograms per deciliter (mcg/dL).

The examples above are common measurements for results for these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens.Talk to your doctor about the meaning of your specific test results.

Higher than normal levels may indicate:

• The pituitary gland near the brain makes too much of the hormone ACTH (called Cushing's disease) because of excess growth of the pituitary gland, or a tumor in the pituitary gland or elsewhere in the body (such as the pancreas, lung, and thyroid)
• Tumor of the adrenal gland that is producing too much cortisol
• Tumor elsewhere in the body that produces cortisol

Lower than normal levels may indicate:

• Addison's disease, when the adrenal glands do not produce enough cortisol
• Hypopituitarism, when the pituitary gland does not signal the adrenal gland to produce enough cortisol

Other conditions under which the test may be performed:

• Acute adrenal crisis
• Ectopic Cushing's syndrome
• Pituitary Cushing's (Cushing's disease) 

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Normally, cortisol levels rise and fall during the day, repeating on a 24-hour cycle (diurnal variation). Highest levels are at about 6 - 8 a.m. and lowest levels are at about midnight.

Physical and emotional stress, as well as illness, can increase cortisol levels, because during the normal stress response the pituitary gland releases more ACTH.

Higher than normal cortisol levels are expected in women who take estrogen or birth control pills.

Stewart PM, Krone NP. The adrenal cortex. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Saunders Elsevier; 2011: chap 15.