Serum or plasma mass concentration of free cortisol

Why This Test Matters

Cortisol is a hormone produced by your adrenal glands that helps regulate metabolism, immune response, and stress reactions. Free cortisol is the active, unbound form that circulates in your bloodstream. This test specifically looks at this free form to avoid interference from proteins that might bind cortisol, ensuring more accurate results.

What to Expect Before the Test

No special preparation is needed for this test. You may have a simple blood draw, where a healthcare provider will collect a small sample from a vein in your arm. If you’re taking medications that affect cortisol levels (like steroids), let your provider know before the test.

Common Uses and Conditions

This test is often used to diagnose or monitor conditions such as Cushing’s syndrome (too much cortisol), adrenal insufficiency (too little cortisol), or to evaluate cortisol fluctuations during stress or sleep.

How the Results Are Interpreted

Results are compared to your baseline or clinical context rather than a single reference range, as cortisol levels can vary widely based on time of day, stress, and individual health. Your healthcare provider will discuss what your results mean in relation to your symptoms and medical history.