Cortisol (AM)

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.

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.

Cortisol normally follows a daily (circadian) rhythm, with levels usually highest in the morning and lowest at night. Because of this pattern, the time of day a sample is taken matters for interpreting your results. Late-night saliva tests and 24-hour urine collections can be especially helpful when your provider is checking for Cushing syndrome, since they capture the natural rise and fall of cortisol throughout the day.

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.

An 8 a.m. cortisol level under roughly 5 to 10 mcg/dL, especially with symptoms like tiredness, weight loss, or low blood pressure, can suggest your body isn't making enough cortisol. Your provider will usually confirm this with a stimulation test before making a diagnosis.

High morning cortisol can be a sign of Cushing's syndrome, but a single morning blood test isn't enough on its own. Providers usually confirm Cushing's with a 24-hour urine cortisol, a late-night saliva cortisol, or a dexamethasone suppression test.

Estrogen — for example, in birth control pills, hormone therapy, or pregnancy — can raise total cortisol in the blood without there being any real problem. This is because estrogen increases the protein that carries cortisol around the body. Your provider may take this into account when reading your result.

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. Cortisol levels can also be affected by other factors, so your provider can help interpret your results.