What Blood Test to Check Cortisol

The blood test to check cortisol levels is primarily the serum cortisol test, often measured in the morning (around 8 a.m.) when cortisol naturally peaks. This test helps diagnose adrenal insufficiency, Cushing’s syndrome, and other hypothalamic-pituitary-adrenal (HPA) axis disorders. Today, clinical guidelines still recommend morning serum cortisol as the first-line screening, with confirmatory tests like the ACTH stimulation test or dexamethasone suppression test when results are borderline. At AnyLabTestNow, we offer a comprehensive cortisol panel that includes these measurements to give you a clear picture of your adrenal health.

Understanding Cortisol and Its Role

Cortisol is a steroid hormone produced by the adrenal glands, often called the “stress hormone.” It regulates metabolism, immune response, blood pressure, and the sleep-wake cycle. Chronically high or low cortisol can signal serious conditions such as Cushing’s disease, Addison’s disease, or adrenal fatigue—a controversial but commonly searched term. Today, functional medicine practitioners increasingly use cortisol testing alongside other biomarkers like DHEA-S and ACTH to assess HPA axis function.

Why a Blood Test Is Preferred

While cortisol can be measured in saliva, urine, or blood, the blood test remains the gold standard for diagnostic accuracy because it directly measures the free and bound hormone in circulation. Serum cortisol is measured in micrograms per deciliter (mcg/dL) and is typically highest between 6 a.m. and 8 a.m. A single low morning value (below 3 mcg/dL) strongly suggests adrenal insufficiency, while a value above 20 mcg/dL may indicate excess cortisol production.

Key Blood Tests for Cortisol

Below are the most common blood tests ordered by healthcare providers in the United States to evaluate cortisol status. Each has a specific clinical purpose.

• Morning Serum Cortisol: Baseline measurement taken between 7 a.m. and 9 a.m. Normal range: 6–23 mcg/dL.
• ACTH Stimulation Test (Cosyntropin Test): Measures cortisol response after synthetic ACTH injection. Used to confirm primary adrenal insufficiency.
• Dexamethasone Suppression Test: Overnight test to diagnose Cushing’s syndrome. Cortisol is measured after taking 1 mg of dexamethasone at 11 p.m.
• Salivary Cortisol (alternative): Sometimes used alongside blood to assess circadian rhythm, but not a blood test.

Comparison of Cortisol Blood Tests

When to Order a Cortisol Blood Test

You may need a cortisol blood test if you experience unexplained weight gain (especially around the abdomen), fatigue, muscle weakness, high blood pressure, mood swings, or easy bruising. Today, telehealth and direct-to-consumer lab testing have made it easier to order cortisol panels without a doctor’s referral. However, interpretation should always be done by a healthcare professional because cortisol levels fluctuate due to stress, illness, medications (like steroids or birth control), and time of day.

Preparing for the Test

Fasting is not typically required, but your provider may ask you to avoid food or caffeine for 8–12 hours before a morning draw. Avoid strenuous exercise and emotional stress 24 hours prior, as both can transiently elevate cortisol. If you are on oral corticosteroids, your doctor may advise holding the dose before testing to get an accurate baseline.

Interpreting Your Results

Low cortisol (hypocortisolism) may point to Addison’s disease, secondary adrenal insufficiency (pituitary issue), or adrenal atrophy. High cortisol (hypercortisolism) may indicate Cushing’s disease, a pituitary tumor, or ectopic ACTH production. Borderline results often require repeat testing or an ACTH stimulation test for confirmation. Today, advanced lab panels also include ACTH, DHEA-S, and renin to provide a full adrenal profile.

Take Control of Your Adrenal Health

Understanding your cortisol levels is the first step toward managing stress, energy, and overall wellness. At AnyLabTestNow, we offer the Cortisol Blood Test Panel—including morning serum cortisol and the ACTH stimulation test—with fast, confidential results. No doctor visit required for ordering. Order your cortisol blood test today and get the answers your body needs.