Serum or plasma free fraction of cortisol concentration (mass concentration)

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms like unexplained weight changes, fatigue, high blood pressure, or signs of adrenal insufficiency (such as low blood pressure upon standing). It may also be used to monitor conditions like Cushing’s syndrome or adrenal gland tumors, or to check how your body responds to cortisol-replacement therapy.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications (like steroids) that could affect cortisol levels for a few days before testing. If you’re taking them, your provider will guide you. You’ll typically have blood drawn in a clinic or lab.

What the Test Results Mean

Results are interpreted based on your symptoms, medical history, and other tests. Elevated free cortisol may suggest conditions like Cushing’s syndrome, while low levels could indicate adrenal insufficiency or other hormonal imbalances. Your provider will discuss these findings with you.

Common Conditions This Test Helps Diagnose

This test supports diagnosing adrenal gland disorders, including hypercortisolism (too much cortisol) or hypocortisolism (too little cortisol). It may also be used in conjunction with other tests to confirm conditions like Cushing’s disease or adrenal tumors.