Cortisol, Free (Serum or Plasma)

Why This Test Is Done

Your doctor may order a free cortisol test to evaluate conditions affecting your adrenal glands, such as Cushing’s syndrome (overproduction of cortisol) or Addison’s disease (underproduction of cortisol). It can also help diagnose adrenal gland tumors or monitor treatment responses for hormone-related disorders.

Sample Collection and Preparation

A blood sample is taken from a vein in your arm. The test measures cortisol in either serum (liquid part of blood after clotting) or plasma (liquid part of blood without clotting). Free cortisol is separated from protein-bound cortisol to provide accurate results.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications or supplements that could affect results. If you’re taking corticosteroids (like prednisone), your doctor may instruct you to stop temporarily or adjust timing.

What the Results Mean

Results are interpreted in the context of your symptoms, medical history, and other tests. Elevated free cortisol levels may indicate Cushing’s syndrome or adrenal tumors, while low levels could signal adrenal insufficiency or other conditions.