Cortisol, Free (Serum or Plasma)

Why Is This Test Done? Your doctor may order this test to help diagnose a medical condition, monitor an ongoing health problem, or check how well a treatment is working for you.

Your healthcare provider may order a free cortisol test to check for conditions like Cushing’s syndrome (when cortisol levels are too high) or adrenal insufficiency (when cortisol levels are too low). It can also help diagnose issues with the pituitary gland or other hormonal imbalances.

What Does the Test Involve? The test typically involves a simple sample collection or imaging procedure performed by trained staff. Your care team will explain each step and answer any questions you have.

A blood sample is taken from a vein in your arm. The test measures cortisol levels in your serum or plasma, which is the liquid part of blood without blood cells. The sample is then analyzed using a sensitive immunoassay method to detect cortisol accurately.

What to Expect Before the Test Before your test, you may receive specific instructions about eating, drinking, or taking your usual medications. Follow these directions carefully, and tell your provider about any allergies or health conditions you have.

No special preparation is usually needed, but you may be asked to avoid certain medications or supplements that could affect cortisol levels, such as steroids or some supplements. If you have a history of bleeding disorders, let your provider know.

What to Expect During the Test During the procedure, a trained technician or nurse will guide you through each step. The test is usually quick and comfortable, and staff will be nearby the entire time to keep you safe and at ease.

The test is quick and typically done in a lab or clinic setting. You’ll have a small needle inserted into your arm, and a few drops of blood will be drawn. The process usually takes a few minutes, and you can resume normal activities afterward.