Cortisol Test

Cortisol is a steroid hormone, which is essential for healthy functioning of the body. Cortisol is produced by the adrenal glands, which are located at the top of the kidneys. A hormone known as ACTH (adrenocorticotropic hormone), which is produced by the pituitary gland, is responsible for stimulating the production and release of cortisol. The body increases levels of cortisol when it is under stress and cortisol also helps to control the immune system. The release of cortisol works in a daily pattern, with levels at their highest at around 8am and their lowest during the evening.

When is the test used?

Cortisol tests are primarily used to diagnose Cushing’s syndrome and Addison’s disease; these are serious conditions, which affect the production of cortisol in the body. Cushing’s syndrome is caused by high levels of cortisol, while Addison’s disease is caused by levels of cortisol which are too low. If tests reveal abnormal concentrations of cortisol in the blood or urine, further tests may be ordered to determine the cause of abnormal production.

The test is usually ordered when a patient has symptoms associated with Cushing’s syndrome or Addison’s disease. Symptoms of Cushing’s syndrome include:

  • High blood pressure
  • Weakness in the muscles
  • Muscle wastage
  • Obesity and unexplained weight gain

Symptoms of Addison’s disease include:

  • Low blood pressure
  • Exhaustion
  • General weakness and a lack of energy
  • The appearance of pigment on the skin

How is the test performed?

The test is done by taking a blood sample from a vein in the arm; a sample is usually taken at 8am at the morning when cortisol levels should be at their highest; the test will then be repeated late at night when levels should be at their lowest. Doing tests at different times of the day allows doctors to evaluate the daily pattern of cortisol secretion.

Urine tests may also be used to measure cortisol levels; this involves a 24 hour test, which measures the secretion of cortisol over a 24 hour period.

What do the test results mean?

High levels of cortisol may indicate that a patient has Cushing’s syndrome, while low levels of cortisol may suggest that a patient has Addison’s disease. If a person has Cushing’s syndrome their daily pattern of cortisol secretion is usually interrupted and irregular and this should be visible on the results of the tests.

If a patient is suspected of having Addison’s disease, further tests will be ordered as the result of the cortisol test is not sufficient to form a diagnosis.

Additional factors such as physical or emotional stress, pregnancy, hyperthyroidism and obesity may also cause cortisol levels to increase.

Specific Blood Tests

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