Your doctor will likely have you do the test early in the morning. This is important, because cortisol level varies throughout the day.
You may be asked not to do any vigorous exercising the day before the test.
You may also be told to temporarily stop taking medicines that can affect the test, including:
Human-made (synthetic) glucocorticoids, such as hydrocortisone, prednisone and prednisolone
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
The test is done to check for increased or decreased cortisol production. Cortisol is a glucocorticoid (steroid) hormone released from the adrenal gland in response to adrenocorticotropic hormone (ACTH). This is a hormone released from the pituitary gland in the brain.
Cortisol affects many different body systems. It plays a role in:
Blood pressure control
Immune system function
Metabolism of fats, carbohydrates, and protein
Nervous system function
Different diseases, such as Cushing syndrome and Addison disease, can lead to either too much or too little production of cortisol. Measuring blood cortisol level can help diagnose these conditions. It is also measured 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 to 23 micrograms per deciliter (mcg/dL).
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.
What Abnormal Results Mean
A higher than normal level may indicate:
Cushing disease, in which the pituitary gland makes too much ACTH because of excess growth of the pituitary gland or a tumor in the pituitary gland
Tumor of the adrenal gland that is producing too much cortisol
A lower than normal level may indicate:
Addison disease, in which the adrenal glands do not produce enough cortisol
Hypopituitarism, in which the pituitary gland does not signal the adrenal gland to produce enough cortisol
Suppression of normal pituitary or adrenal function by glucocorticoid medications including pills, skin creams, eyedrops, inhalers, joint injections, chemotherapy
Other conditions for which the test may be ordered include:
Acute adrenal crisis
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:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Guber HA, Farag AF. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 24.
Stewart PM, Krone NP. The adrenal cortex. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 15.
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.