What is plasma cortisol?

Plasma cortisol is a laboratory test used to determine the levels of the hormone cortisol in the blood. Cortisol levels can provide important information about a patient's health and can be used in the diagnosis and management of a number of conditions, most related to the adrenal gland, the site where cortisol is produced. In a plasma cortisol test, blood is drawn from a patient and analyzed in the laboratory. Multiple samples can be requested.

In healthy individuals, the adrenal gland produces cortisol to help with a number of metabolic functions. Levels of this hormone in the body fluctuate throughout the day, with evening levels typically being about half of those in the morning. If levels are unusually high or low, it may be an indicator that a patient has a condition such as Cushing's disease, Addison's disease, or adrenal insufficiency. High levels can also be an indicator of stress, as cortisol tends to increase in response to stress.

Prior to a plasma cortisol test, patients may be advised to eat and exercise normally, fasting for approximately 12 hours before the blood sample is drawn. If possible, patients should stop taking medications that can influence cortisol levels for two days before the test. If doing so would jeopardize the patient's health because those drugs are necessary for survival, the patient may continue to use them and a note will be made so that lab technicians are aware of the possibility of biased results.

A common procedure is to draw one sample in the morning and one at night. Plasma cortisol levels will be compared both to determine if they are within the normal range and to see if they fall over the course of the day, as expected. This is an outpatient procedure, with patients leaving after the blood draw. Depending on the results, additional tests may be ordered or a physician may discuss options for management of abnormal plasma cortisol levels.

When this test is recommended, patients can ask their doctors why and learn more about how plasma cortisol is relevant to their diagnosis and treatment. This test is applied in different ways and being aware of what the doctor is looking for can help patients prepare more adequately. It is also important to review the symptoms currently being experienced, as these can provide important clues as to the nature of the patient's condition.

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