Cortisol (Late Night Salivary)

Your pituitary gland, a gland in your brain, makes another hormone, called ACTH (adrenocorticotropic hormone). ACTH tells your adrenal glands how much cortisol to make. If your cortisol levels are too high or too low, it may mean you have a problem with your adrenal glands or your pituitary gland.

In healthy people, cortisol follows a daily pattern - levels are highest in the early morning and drop to their lowest in the late evening or middle of the night. In Cushing syndrome, this nighttime dip is lost, so cortisol stays high. Late-night salivary cortisol takes advantage of this pattern: a saliva sample is collected at home around bedtime, when cortisol should be at its lowest.

High cortisol levels may also be caused by a tumor that makes cortisol, or taking large doses of certain steroid medicines, such as prednisone, for a long time. Low levels may happen if you stop the medicine suddenly. Without treatment, cortisol levels that are too high or too low can be very serious.

A cortisol test alone can't diagnose the cause of abnormal cortisol levels. If your cortisol level isn't normal, you will usually have more tests to find out what is causing the problem.

A high late-night salivary cortisol level (above the lab's reference range) suggests that the normal nighttime drop in cortisol is missing, which is a common feature of Cushing syndrome. Because one high result is not enough on its own, providers usually repeat the test on another night and may add other cortisol tests before making a diagnosis.

A normal late-night salivary cortisol level makes Cushing syndrome much less likely, but does not fully rule it out, especially in mild cases.

Low levels may mean you have Addison disease or secondary adrenal insufficiency.

If your cortisol results aren't normal, it doesn't always mean you have a medical condition that needs treatment. The most common cause of abnormal cortisol levels is taking steroid medicines for a long time or suddenly stopping them. Shift work, poor sleep, depression, alcohol use, or recent acute illness can also affect this test.