Serum or plasma concentration of free cortisol

Why This Test Is Done

Your doctor may order a free cortisol test to check for hormonal imbalances, such as whether your adrenal glands are producing too much or too little cortisol. It can also help evaluate conditions like Cushing’s syndrome (caused by high cortisol) or adrenal insufficiency (low cortisol).

How the Test Works

Blood is drawn from a vein, usually in your arm. The sample is then processed to separate free cortisol from protein-bound cortisol. The test measures only the free (unbound) portion, which reflects your active cortisol levels in the bloodstream.

Sample Collection and Preparation

For this test, you’ll have a small needle inserted into a vein to collect blood. The sample is sent to a lab for analysis. Free cortisol is typically measured using a sensitive immunoassay method to ensure accurate results.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications or supplements that could affect cortisol levels, such as some steroids or herbal products. Stress or recent illness might temporarily alter results, so inform your doctor if you’ve had recent changes in health.