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The Test Sample
What is being tested?
Cortisol is a hormone that plays a role in the metabolism of proteins, lipids, and carbohydrates. It affects blood glucose levels, helps maintain blood pressure, and helps regulate the immune system. Most cortisol in the blood is bound to a protein; only a small percentage is "free" and biologically active. Free cortisol is secreted into the urine and is present in the saliva. This test measures the amount of cortisol in the blood, urine, or saliva.
The level of cortisol in the blood (as well as the urine and saliva) normally rises and falls in a "diurnal variation" pattern. It peaks early in the morning, then declines throughout the day, reaching its lowest level about midnight. This pattern can change when a person works irregular shifts (such as the night shift) and sleeps at different times of the day, and it can become disrupted when a disease or condition either limits or stimulates cortisol production.
Cortisol is produced and secreted by the adrenal glands, two triangular organs that sit on top of the kidneys. 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.
- Administration of large amounts of glucocorticosteroid hormones (such as prednisone, prednisolone, or dexamethasone) to treat a variety of conditions, such as autoimmune disease and some tumors
- ACTH-producing tumors, in the pituitary gland and/or in other parts of the body
- Increased cortisol production by the adrenal glands, due to a tumor or due to excessive growth of adrenal tissues (hyperplasia)
- Rarely, with tumors in various parts of the body that produce CRH
Decreased cortisol production may be seen with:
- An underactive pituitary gland or a pituitary gland tumor that inhibits ACTH production; this is known as secondary adrenal insufficiency.
- Underactive or damaged adrenal glands (adrenal insufficiency) that limit cortisol production; this is referred to as primary adrenal insufficiency and is also known as Addison disease.
- After stopping treatment with glucocorticosteroid hormones, especially if stopped very quickly after a long period of use
How is the sample collected for testing?
Typically, blood will be drawn from a vein in the arm, but sometimes urine or saliva may be tested. Cortisol blood tests may be drawn at about 8 am, when cortisol should be at its peak, and again at about 4 pm, when the level should have dropped significantly.
Sometimes a resting sample will be obtained to measure cortisol when it should be at its lowest level (just before sleep); this is often done by measuring cortisol in saliva rather than blood to make it easier to obtain the sample. Saliva for cortisol testing is usually collected by inserting a swab into the mouth and waiting a few minutes while the swab becomes saturated with saliva. Obtaining more than one sample allows the health practitioner to evaluate the daily pattern of cortisol secretion (the diurnal variation).
Sometimes urine is tested for cortisol; this usually requires collecting all of the urine produced during a day and night (a 24-hour urine) but sometimes may be done on a single sample of urine collected in the morning.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Some test preparation may be needed. Follow any instructions that are given as far as timing of sample collection, resting, and/or any other specific pre-test preparation.
A saliva test requires special care in obtaining the sample. You may be instructed to refrain from eating, drinking, or brushing your teeth for a period of time (may be some time between 15 to 30 minutes) prior to the test. Follow any specific instructions that are provided.
A stimulation or suppression test requires that you have a baseline blood sample drawn and then a specified amount of drug is given. Subsequent blood samples are drawn at specified times.