Cortisol, Free (Serum or Plasma)

Why This Test Is Done

Your doctor may order a free cortisol test to check for conditions like Cushing’s syndrome (overactive adrenal glands causing high cortisol) or adrenal insufficiency (low cortisol levels). It can also help diagnose issues with the pituitary gland or adrenal glands, especially if symptoms like fatigue, weight changes, or mood swings are present.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves a blood draw. If you’re taking medications that affect cortisol levels, your doctor will let you know whether to stop them temporarily.

During the Test

A healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but it typically only takes a few minutes. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are compared to standard reference ranges, but they can vary based on the lab and testing method. High cortisol levels may indicate conditions like Cushing’s syndrome, while very low levels could signal adrenal problems or other hormonal imbalances. Your doctor will interpret the results in the context of your symptoms and medical history.