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A cortisol level test uses a blood sample to measure the level of cortisol in your blood.
Cortisol is a steroid hormone produced by the adrenal glands. Whenever you experience something your body perceives as a threat, like a large dog barking at you, a chemical known as adrenocorticotropic hormone (ACTH) is released in your brain. This triggers your adrenal glands to release cortisol and adrenaline.
Cortisol is the main hormone involved in stress and the fight, flight, or freeze response. This is a natural and protective response to a perceived threat or danger. Increased levels of cortisol result in a burst of new energy and strength.
In the fight, flight, or freeze response, cortisol suppresses any functions that are unnecessary or detrimental to that response. During a fight, flight, or freeze response, you can have:
- a rapid heart rate
- dry mouth
- stomach upset
Cortisol release also:
- suppresses your growth processes
- suppresses your digestive system
- suppresses your reproductive system
- changes how your immune system responds
The cortisol level test checks whether your cortisol production levels are too high or too low. Certain conditions, such as Addison’s disease and Cushing’s disease, affect the amount of cortisol your adrenal glands produce.
The test is used in the diagnosis of these diseases and as a way to assess the functioning of the adrenal and pituitary glands.
Cortisol plays a role in several systems in the body, including:
- stress responses
- immune system
- nervous system
- circulatory system
- skeletal system
- the breakdown of proteins, fats, and carbohydrates
A blood sample is used to measure cortisol levels. Most blood samples are collected using this process:
- The flow of blood in the arm is stopped by wrapping an elastic band around your upper arm. This also causes the veins in your arm to become more visible, making it easier to insert the needle.
- Alcohol is used to clean the site on your skin where the needle will be inserted.
- The needle is inserted into the vein. This may cause a brief pinching or stinging sensation.
- Your blood is collected in a tube that’s attached to the needle. More than one tube may be needed.
- The elastic band is removed after enough blood has been collected.
- As the needle is removed from your skin, cotton or gauze is placed on the site of the needle insertion.
- Pressure is applied to the area using cotton or gauze. A bandage is used to secure the cotton or gauze.
There are few risks associated with the cortisol level test. The test is done by taking a blood sample from your vein, which may result in some bruising at the site where the needle was inserted.
In rare cases, the following risks may be associated with having blood drawn from your vein:
- excessive bleeding
- an accumulation of blood beneath your skin, which is called a hematoma
- lightheadedness or fainting
Cortisol levels vary throughout the day but are usually highest in the morning. Your doctor will usually request that the test be done in the morning. You don’t need to fast for a cortisol test.
Certain drugs affect cortisol levels. Your doctor may request that you not take these drugs before the test is done. Cortisol levels are sometimes increased by:
- drugs containing estrogen
- synthetic glucocorticoids, such as prednisone
Cortisol levels are sometimes decreased by:
- drugs containing androgens
Cortisol levels can also be affected by physical and emotional stress and illness. This is due to the increased release of ACTH by the pituitary gland during the usual stress response.
Standard results for a blood sample taken at 8 a.m. range between 6 and 23 micrograms per deciliter (mcg/dL). Many laboratories have different measuring techniques, and what’s considered standard may vary.
Higher-than-usual cortisol levels may indicate that:
- your pituitary gland is releasing too much ACTH due to a tumor or excess growth of the pituitary gland
- you have a tumor in your adrenal gland, resulting in excess cortisol production
- you have a tumor elsewhere in your body that’s involved in cortisol production
Lower-than-usual cortisol levels may indicate that:
- you have Addison’s disease, which occurs when the production of cortisol by your adrenal glands is too low
- you have hypopituitarism, which occurs when the production of cortisol by your adrenal glands is too low because the pituitary gland is not sending proper signals
Your doctor will go over your test with you. They may order more tests if they believe cortisol levels in your blood are too high or too low.