Serum/plasma concentration of free (unbound) cortisol

Why This Test Matters

Cortisol is a hormone produced by your adrenal glands that helps your body respond to stress. Free cortisol is the portion that’s available to your body’s cells, not bound to proteins. Measuring it can help identify whether your cortisol levels are too high or too low, which may indicate hormonal imbalances or other health issues.

When You Might Need This Test

Your doctor may order this test if you have symptoms like unexplained weight changes, fatigue, high blood pressure, or signs of hormonal disorders. It’s also used in diagnosing conditions like Cushing’s syndrome (too much cortisol) or adrenal insufficiency (too little cortisol).

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 you’re taking medications that affect cortisol levels, your doctor will let you know if you need to stop them temporarily.

What Happens During the Test

A healthcare professional will draw blood from a vein in your arm. The blood will be sent to a lab for analysis. The test typically takes a few minutes, and you may feel a slight pinch during the draw.