Cortisol, Serum (Free Cortisol)

Why This Test Might Be Ordered

Your healthcare provider may order a free cortisol test to diagnose or monitor conditions like Cushing’s syndrome (a hormonal disorder caused by excess cortisol), adrenal insufficiency (when your adrenal glands don’t produce enough cortisol), or to evaluate stress responses, especially if symptoms such as 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 a few hours before the blood draw if cortisol levels are being measured at specific times of the day. If you’re taking medications that affect cortisol levels, let your provider know.

What the Test Involves

A healthcare professional will draw blood from a vein in your arm. The blood sample is then sent to a lab for analysis. Free cortisol is measured using a sensitive immunoassay method to detect its presence in your serum.

What the Results Mean

Results are typically reported as a concentration of cortisol in your blood. While reference ranges can vary slightly between labs, elevated or low levels may indicate underlying health concerns that need further evaluation by your doctor.