Plasma cortisol is a laboratory test used to determine levels of the hormone cortisol in the blood. Cortisol levels can provide important information about a patient's health and may 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 lab. Several samples may be requested.
In healthy individuals, the adrenal gland makes cortisol to aid with a number of metabolic functions. Levels of this hormone in the body fluctuate over the course of the day, with afternoon levels typically being about half those in the morning. If the levels are unusually high or low, it can be an indicator that a patient has a condition like Cushing's disease, Addison's disease, or adrenal insufficiency. High levels can also be an indicator of stress, as cortisol tends to rise in response to stress.
Before a plasma cortisol test, patients may be advised to eat and exercise normally, fasting for around 12 hours before the blood sample is taken. If possible, patients will need to stop taking medications that might influence cortisol levels for two days before the test. If doing this would put the patient's health at risk because those medications are needed for survival, the patient can continue using them and a note will be made so laboratory technicians are aware of the potential for skewed results.
A common procedure involves drawing a sample in the morning and another in the evening. The plasma cortisol levels will be compared both to determine if they are within 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 requested or a doctor may discuss options for management of abnormal plasma cortisol levels.
When this test is recommended, patients may want to ask their doctors why and get more information about how plasma cortisol is relevant to their diagnosis and treatment. This test is applied in a number of different ways and being aware of what the doctor is looking for can help patients prepare more adequately. It's also important to go over any symptoms currently being experienced, as they can provide important clues to the nature of a patient's condition.