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Tests & Procedures : Lab Tests

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Cortisol (Blood)

Does this test have other names?

Blood cortisol; cortisol, blood; plasma cortisol; cortisol, plasma

What is this test?

A serum cortisol test may help in the diagnosis of two fairly uncommon medical conditions: Cushing's syndrome and Addison's disease. The test also screens for other diseases that affect your pituitary and adrenal glands. It does so by measuring your blood level of a stress hormone called cortisol.

Cortisol is a steroid hormone made by your adrenal glands. It helps your body respond to stress, regulate blood sugar, and fight infections. In most people, cortisol levels are highest in the morning when they wake up and lowest around midnight. Your body also pumps out excess cortisol when you're anxious or under intense stress, which can affect your health if the levels stay too high for too long. If your cortisol levels are too high or too low, you may have a condition that needs treatment. 

Why do I need this test?

You may need this test if your health care provider suspects a medical problem caused by too much or too little cortisol.

A high cortisol level could be a sign of Cushing's syndrome. Symptoms of Cushing's syndrome include:

  • Obesity, especially in the torso, face, and neck, with thinner arms and legs

  • High blood pressure

  • High blood sugar

  • Thin skin that bruises easily

  • Pink or purple streaks on the stomach, thighs, or buttocks

  • Muscle weakness

  • Osteoporosis

  • Acne

  • For women, irregular menstrual periods and excess hair on the face and chest

Too little cortisol could be a sign of Addison's disease, also called primary adrenal insufficiency. It could also be a sign of another problem with your adrenal glands. This may cause these symptoms:

  • Weight loss

  • Muscle and joint pain

  • Fatigue, or extreme tiredness

  • Low blood pressure

  • Abdominal (belly) pain

  • Nausea and/or vomiting

  • Diarrhea

  • Dark patches of skin

  • For women, decreased armpit and pubic hair and decreased sexual desire

You may also need this test if your doctor suspects an adrenal crisis. This can be a life-threatening emergency. Symptoms include:

  • Shock, or very low blood pressure and loss of consciousness

  • Dehydration

  • Sudden, severe abdominal (belly) pain

  • Vomiting and diarrhea

  • Weakness and tiredness

  • Confusion 

What other tests might I have along with this test?

Besides a blood test for cortisol, your health care provider may test the cortisol levels in your urine or saliva.

Your doctor will likely order other blood tests that measure your body's response to certain hormones to help determine the cause of your abnormal cortisol levels.

You may also have tests to look inside your body for abnormal growths or tumors. These can affect cortisol levels. Tests may include:

  • CT scan

  • MRI scan 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Your test result will tell you the level of cortisol in your blood at the time of the test. Normal cortisol levels are usually highest early in the morning and lowest about midnight. Normal ranges vary depending on the type of test. For most tests, normal ranges are:

  • 6 to 8 a.m.: 10 to 20 micrograms per deciliter (mcg/dL)

  • Around 4 p.m.: 3 to 10 mcg/dL

Abnormal cortisol levels are often caused by long-term use of glucocorticoid medicines, such as those taken to control asthma, autoimmune diseases, or inflammation. If this is the cause, your doctor may gradually reduce your doses of these medicines.   

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.  The timing of the test is important, because cortisol levels change throughout the day. It's common to test serum cortisol twice in the same day – early in the morning and again around 4 p.m.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

Your cortisol levels change in response to many events. For instance, if you work nights and sleep during the day, your cortisol levels may not be in the normal range.

Your cortisol levels may be higher than normal because of physical trauma and stress. Women in their last three months of pregnancy and highly trained athletes may have higher-than-normal levels of cortisol. Other reasons your cortisol level may be higher than normal include depression, alcoholism, malnutrition, and a panic disorder.

A number of medications, especially oral contraceptives and any medication that contains glucocorticoids, or steroid hormones similar to cortisol, can also affect your cortisol levels.

How do I get ready for this test?

You may need to rest before the test to keep stress levels down. You will also need to avoid medications that can affect the results of the test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.