A cortisol test is done to measure the level of the hormone cortisol in the blood. The cortisol level may show problems with the adrenal glands or pituitary gland. Cortisol is made by the adrenal glands . Cortisol levels go up when the pituitary gland releases another hormone called adrenocorticotropic hormone (ACTH).
Cortisol has many functions. It helps the body use sugar (glucose) and fat for energy (metabolism), and it helps the body manage stress. Cortisol levels can be affected by many conditions, such as physical or emotional stress, strenuous activity, infection, or injury.
Normally, cortisol levels rise during the early morning hours and are highest about 7 a.m. They drop very low in the evening and during the early phase of sleep. But if you sleep during the day and are up at night, this pattern may be reversed. If you do not have this daily change (diurnal rhythm) in cortisol levels, you may have overactive adrenal glands. This condition is called Cushing's syndrome.
The timing of the cortisol test is very important because of the way cortisol levels vary throughout a day. If your doctor thinks you might make too much cortisol, the test will probably be done late in the day. If your doctor thinks you may not be making enough, a test is usually done in the morning.
Why It Is Done
A cortisol test is done to find problems of the pituitary gland or adrenal glands, such as making too much or too little hormones.
How To Prepare
Many medicines may change the results of this test. Some medicines, such as steroids, can affect cortisol levels for some time even after you stop taking the medicine. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure to the site and then a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
A cortisol test is done to measure the level of the hormone cortisol in the blood.
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
3-16 mcg/dL or 83-441 nmol/L
2-11 mcg/dL or 55-304 nmol/L
- A high level of cortisol in the blood can mean Cushing's syndrome, a disorder that can be caused by overactive adrenal glands, an adrenal gland tumor, some types of cancer, or long-term use of corticosteroids.
- A high blood cortisol level can be caused by severe liver or kidney disease, depression, hyperthyroidism, or obesity.
- Pregnancy or birth control pills can also cause a high blood cortisol level.
- Conditions such as recent surgery, illness, injury, or whole-body infection (sepsis) can cause high cortisol levels.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Having physical or emotional stress.
- Being pregnant. This can cause urine cortisol levels to be high.
- Having low blood sugar (hypoglycemia).
- Eating, drinking, or exercising before the test.
- Taking medicines, such as birth control pills, estrogen, amphetamines, or corticosteroids.
- Having a radioactive scan within 1 week of a cortisol test.
What To Think About
- A 24-hour urine test is used more often than a cortisol blood test to diagnose Cushing's syndrome. To learn more about cortisol in urine, see the topic Cortisol in Urine.
- Other tests that can help determine if the pituitary gland or adrenal glands are functioning properly include the adrenocorticotropic hormone (ACTH) stimulation test and dexamethasone suppression tests. The ACTH stimulation test may be done when Addison's disease is suspected.
To learn more, see:
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerAlan C. Dalkin, MD - Endocrinology
Current as ofNovember 20, 2015