Cortisol, Free, Serum

Why This Test Is Done

Your doctor may order a free cortisol test if you have symptoms of hormonal imbalances, such as unexplained weight changes, fatigue, high blood pressure, or unusual mood swings. It can also be used to monitor conditions like adrenal gland tumors or to check for cortisol overproduction (Cushing’s syndrome) or deficiency.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if timing your results around a specific time of day (morning is most common). Avoid caffeine or stressful activities for a few hours before testing.

How the Test Is Performed

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but the procedure is quick and usually painless. The blood sample is sent to a lab for analysis using an immunoassay method to detect cortisol levels.

What the Results Mean

Results are compared to general reference ranges, but interpretation depends on timing (e.g., morning vs. evening) and clinical context. Elevated levels may suggest Cushing’s syndrome or other adrenal issues, while low levels could indicate adrenal insufficiency or other disorders.