A cortisol test may be used to help diagnose Cushing syndrome, a condition associated with excess cortisol, or to help diagnose adrenal insufficiency or Addison disease, conditions associated with deficient cortisol. Cortisol is a hormone that plays a role in the metabolism of proteins, lipids, and carbohydrates, among other functions. Normally, the level of cortisol in the blood rises and falls in a "diurnal variation" pattern, peaking early in the morning, then declining throughout the day and reaching its lowest level about midnight.

Cortisol is produced and secreted by the adrenal glands. Production of the hormone is regulated by the hypothalamus in the brain and by the pituitary gland, a tiny organ located below the brain. When the blood cortisol level falls, the hypothalamus releases corticotropin-releasing hormone (CRH), which directs the pituitary gland to produce ACTH (adrenocorticotropic hormone). ACTH stimulates the adrenal glands to produce and release cortisol. In order for appropriate amounts of cortisol to be made, the hypothalamus, the pituitary, and the adrenal glands must be functioning properly. (See the "What is being tested?" section for more.)

Most cortisol in the blood is bound to a protein; only a small percentage is "free" and biologically active. Blood cortisol testing evaluates both protein-bound and free cortisol while urine and saliva testing evaluate only free cortisol, which should correlate with the levels of free cortisol in the blood. Multiple blood and/or saliva cortisol levels collected at different times, such as at 8 am and 4 pm, can be used to evaluate both cortisol levels and diurnal variation. A 24-hour urine cortisol sample will not show diurnal variation; it will measure the total amount of unbound cortisol excreted in 24 hours.

If an abnormal level of cortisol is detected, a health practitioner will do additional testing to help confirm the findings and to help determine its cause:

Testing for Excess Cortisol Production
If a person has a high blood cortisol level, a health practitioner may perform additional testing to confirm that the high cortisol is truly abnormal (and not simply due to increased stress or the use of cortisol-like medication). This additional testing may include measuring the 24-hour urinary cortisol, doing an overnight dexamethasone suppression test, and/or collecting a salivary sample before retiring in order to measure cortisol at the time that it should be the lowest. Urinary cortisol requires the collection of urine over a timed period, usually 24 hours. Since ACTH is secreted by the pituitary gland in pulses, this test helps determine whether the elevated blood cortisol level represents a real increase.

Dexamethasone suppression: The dexamethasone suppression test involves analyzing a baseline sample for cortisol, then giving the person oral dexamethasone (a synthetic glucocorticoid) and measuring cortisol levels in subsequent timed samples. Dexamethasone suppresses ACTH production and should decrease cortisol production if the source of the excess is stress.

Collecting a salivary sample for cortisol measurement is a convenient way to determine whether the normal rhythm of cortisol production is altered. If one or more of these tests confirms that there is abnormal cortisol production, then additional testing, including measuring ACTH, repeating the dexamethasone suppression test using higher doses, and radiologic imaging may be ordered.

Testing for Insufficient Cortisol Production
If a health practitioner suspects that the adrenal glands may not be producing adequate cortisol or if the initial blood tests indicate insufficient cortisol production, the health practitioner may order an ACTH stimulation test.

ACTH stimulation: This test involves measuring the level of cortisol in a person's blood before and after an injection of synthetic ACTH. If the adrenal glands are functioning normally, then cortisol levels will rise with the ACTH stimulation. If they are damaged or not functioning properly, then the cortisol level will be low. A longer version of this test (1-3 days) may be performed to help distinguish between adrenal and pituitary insufficiency.

A cortisol test may be ordered when a person has symptoms that suggest a high level of cortisol and Cushing syndrome, such as

• High blood pressure (hypertension)
• High blood sugar (glucose)
• Obesity, especially in the trunk
• Fragile skin
• Purple streaks on the abdomen
• Muscle wasting and weakness
• Osteoporosis

Testing may be ordered when women have irregular menstrual periods and increased facial hair; children may have delayed development and a short stature.

This test may be ordered when someone has symptoms suggestive of a low level of cortisol, adrenal insufficiency or Addison disease, such as:

• Weight loss
• Muscle weakness
• Fatigue
• Low blood pressure
• Abdominal pain
• Dark patches of skin (this occurs in Addison disease but not secondary adrenal insufficiency)

Sometimes decreased production combined with a stressor can cause an adrenal crisis that can be life-threatening and requires immediate medical attention. Symptoms of a crisis may include:

• Sudden onset of severe pain in the lower back, abdomen, or legs
• Vomiting and diarrhea, resulting in dehydration
• Low blood pressure (hypotension)
• Loss of consciousness

Suppression or stimulation testing is ordered when initial findings are abnormal. Cortisol testing may be ordered at intervals after a diagnosis of Cushing syndrome or Addison disease to monitor the effectiveness of treatment.

Normally, cortisol levels are very low at bedtime and at their highest just after waking, though this pattern will change if a person works rotating shifts and sleeps at different times on different days.

An increased or normal cortisol level just after waking along with a level that does not drop by bedtime suggests excess cortisol and Cushing syndrome. If this excess cortisol is not suppressed after an overnight dexamethasone suppression test, or if the 24-hour urine cortisol is elevated, or if the late-night salivary cortisol level is elevated, it suggests that the excess cortisol is due to abnormal increased ACTH production by the pituitary or a tumor outside of the pituitary or abnormal production by the adrenal glands. Additional testing will help to determine the exact cause. (See the section "How is it used?" above.)

If insufficient cortisol is present and the person tested responds to an ACTH stimulation test, then the problem is likely due to insufficient ACTH production by the pituitary. If the person does not respond to the ACTH stimulation test, then it is more likely that the problem is based in the adrenal glands. If the adrenal glands are underactive, due to pituitary dysfunction and/or insufficient ACTH production, then the person is said to have secondary adrenal insufficiency. If decreased cortisol production is due to adrenal damage, then the person is said to have primary adrenal insufficiency or Addison disease.

Once an abnormality has been identified and associated with the pituitary gland, adrenal glands, or other cause, then the health practitioner may use other testing such as CT (computerized tomography) or MRI (magnetic resonance imaging) scans to locate the source of the excess (such as a pituitary, adrenal, or other tumor) and to evaluate the extent of any damage to the glands.

Similar to those with adrenal insufficiency, people with a condition called congenital adrenal hyperplasia (CAH) have low cortisol levels and do not respond to ACTH stimulation tests. Cortisol measurement is one of many tests that may be used to help evaluate a person for CAH.

Heat, cold, infection, trauma, exercise, obesity, and debilitating disease can influence cortisol concentrations. Pregnancy, physical and emotional stress, and illness can increase cortisol levels. Cortisol levels may also increase as a result of hyperthyroidism or obesity. A number of drugs can also increase levels, particularly oral contraceptives (birth control pills), hydrocortisone (the synthetic form of cortisol), and spironolactone.

Adults have slightly higher cortisol levels than children do.

Hypothyroidism may decrease cortisol levels. Drugs that may decrease levels include some steroid hormones.

Salivary cortisol testing is being used more frequently to help diagnose Cushing syndrome and stress-related disorders but still requires specialized expertise to perform.