Cortisol levels are tested through blood draws, saliva samples, or 24-hour urine collections, depending on what your doctor suspects. A standard morning blood test is the most common starting point, with normal levels falling between 10 and 20 mcg/dL when drawn between 6 and 8 a.m. From there, more specialized tests can confirm whether your body is producing too much or too little cortisol.
Why Timing Matters for Every Cortisol Test
Cortisol follows a predictable daily rhythm. It peaks in the early morning, helping you wake up, then gradually drops throughout the day. By 4 p.m., normal blood levels fall to roughly 3 to 10 mcg/dL, about half of the morning value. By late evening, cortisol should be at its lowest point of the entire day.
This natural curve is the basis for nearly every cortisol test. A morning blood draw checks whether your body is producing enough cortisol at its expected peak. A late-night saliva test checks whether cortisol is dropping the way it should. If your doctor orders a test at a specific time, that timing isn’t flexible. A sample collected at the wrong hour can look abnormally high or low simply because of where you are in the daily cycle, not because anything is actually wrong.
Morning Blood Test
The simplest cortisol test is a blood draw, typically scheduled between 6 and 8 a.m. to catch cortisol near its daily peak. A nurse draws blood from a vein in your arm, and results usually come back within a day or two. The expected range at that hour is 10 to 20 mcg/dL, though labs may vary slightly in their reference values.
Because stress can spike cortisol quickly, you may be asked to sit quietly for 15 to 30 minutes before the draw. Even the anxiety of a needle stick can temporarily raise levels, which is one reason doctors sometimes prefer saliva or urine tests for a fuller picture.
Late-Night Saliva Test
A late-night salivary cortisol test is one of the primary screening tools for Cushing syndrome, a condition caused by prolonged excess cortisol. The logic is simple: cortisol should be at its lowest around midnight. If it’s still elevated at that hour, something may be overriding the normal daily drop.
You collect the sample at home, typically between 11 p.m. and midnight, by placing a small swab or cotton roll in your mouth. For 30 minutes before collecting, don’t eat, drink, brush your teeth, floss, smoke, or vape. Any of these can contaminate the sample or stimulate saliva in ways that alter the reading.
This test has a reported sensitivity and specificity above 90% for detecting certain forms of Cushing syndrome. However, a single elevated result doesn’t confirm a diagnosis. Most people with one high late-night reading turn out not to have Cushing syndrome, so doctors typically repeat the test at least once before moving to more involved evaluations.
24-Hour Urine Collection
A 24-hour urine test measures your total cortisol output over an entire day, smoothing out the natural peaks and dips that can make a single blood draw hard to interpret. The normal range is 10 to 100 mcg per 24 hours.
The collection process takes some planning. On the morning you start, you urinate into the toilet as usual, then collect every subsequent sample in a special container for the next 24 hours. The following morning, your first urination goes into the container, completing the cycle. Keep the container refrigerated or in a cool place throughout. Label it with your name, the date, and the time you finished, then return it to the lab.
Missing even one sample during the 24 hours can throw off results, so most people find it easiest to stay home for the collection day. Elevated levels on this test can point toward Cushing syndrome, while unusually low levels may suggest adrenal insufficiency.
Dexamethasone Suppression Test
This test checks whether your body’s cortisol production responds normally to a signal that should shut it down. You take a small pill (a synthetic steroid) at 11 p.m., and your blood is drawn the next morning at 8 a.m. In a healthy system, that pill tells your brain to stop requesting cortisol, and morning levels drop below 1.8 mcg/dL. If cortisol stays elevated despite the signal, it suggests something is producing cortisol independently, whether a pituitary issue or an adrenal problem.
This is a confirmatory test, not a first step. Doctors order it after screening tests like saliva or urine suggest excess cortisol.
ACTH Stimulation Test
While the tests above look for too much cortisol, the ACTH stimulation test checks whether your adrenal glands can produce enough. A healthcare provider injects a synthetic version of the hormone that normally tells your adrenal glands to release cortisol, then measures your blood cortisol at timed intervals, usually 30 and 60 minutes later.
A normal response means cortisol rises above 15 to 16 mcg/dL after the injection. If it stays flat or barely rises, your adrenal glands aren’t responding properly, which can indicate adrenal insufficiency (sometimes called Addison’s disease) or problems with the pituitary gland.
What Can Skew Your Results
Several everyday factors can push cortisol readings higher or lower than your true baseline. Stress, vigorous exercise, illness, and even exposure to extreme temperatures all raise cortisol. Poor sleep or an unusual sleep schedule shifts the daily rhythm, making timed tests unreliable.
Medications are the biggest source of false results. Oral contraceptives containing estrogen increase a protein in the blood that binds to cortisol, raising the total cortisol measurement without actually increasing the active cortisol your body uses. In studies of the dexamethasone suppression test, up to 50% of women on oral contraceptives received false-positive results, meaning the test incorrectly suggested excess cortisol. Anti-seizure medications, certain antibiotics, and any steroid-containing product (including creams, inhalers, and joint injections) can also interfere. Tell your doctor about every medication and supplement you take before any cortisol test.
Most doctors will ask women to stop oral contraceptives for at least six weeks before cortisol testing if possible, since the protein changes take time to normalize.
At-Home Cortisol Kits
Several companies sell saliva-based cortisol kits that you can order online and complete at home. These typically collect multiple samples throughout the day to map your cortisol curve. The saliva collection method itself is the same one used in clinical settings, and the samples are mailed to a lab for analysis.
The limitation is interpretation. A single cortisol value without clinical context doesn’t tell you much. Levels fluctuate with stress, sleep, food, and dozens of other variables. An out-of-range result from a home kit can’t distinguish between a stressful week and a genuine endocrine disorder. If you’re concerned enough to test, the results will still need a doctor’s evaluation to mean anything actionable. Starting with your primary care provider, who can order the right test for your specific symptoms, is generally more efficient than screening yourself first.
Which Test You’ll Likely Get
Your symptoms guide which test your doctor orders. If you have signs of excess cortisol (unexplained weight gain concentrated in the face and midsection, easy bruising, purple stretch marks, high blood sugar), you’ll typically start with a late-night saliva test or 24-hour urine collection. If you have signs of low cortisol (extreme fatigue, dizziness, unintentional weight loss, darkening skin), the ACTH stimulation test is the standard first step. A routine morning blood draw often serves as the initial screen in either direction, helping your doctor decide which specialized test to pursue next.