Cortisol (serum/plasma) concentration

Why This Test Is Done

Your healthcare provider may order cortisol testing to evaluate symptoms such as unexplained weight changes, fatigue, high blood pressure, or unusual hair growth. It can also be used to diagnose hormonal imbalances, such as Cushing’s syndrome (too much cortisol) or Addison’s disease (too little cortisol). Sometimes, cortisol levels are checked during a stress test, like the overnight dexamethasone suppression test, to further investigate suspected adrenal issues.

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, let your provider know. If you’re undergoing a stress test (e.g., dexamethasone suppression), follow all instructions precisely, including timing of medications and activities.

How the Test Is Done

A healthcare professional will draw blood from a vein in your arm. The blood sample is sent to a lab for analysis. If cortisol is measured in urine over 24 hours, you’ll need to collect all urine for a full day and return it to the lab.

What the Results Mean

Results are compared to standard ranges, but individual ranges can vary by lab. High cortisol levels may indicate conditions like Cushing’s syndrome, while very low levels could signal adrenal insufficiency or other hormonal disorders. Your provider will interpret results in the context of your symptoms and medical history.