Cortisol is measured through blood, saliva, urine, or hair samples, and the right test depends on what your doctor is looking for. A single morning blood draw is the most common starting point, but because cortisol levels shift dramatically throughout the day, one sample rarely tells the whole story. Most evaluations involve at least two different tests or collection times to build an accurate picture.
Why Timing Matters for Every Test
Cortisol follows a predictable daily rhythm. Levels are highest when you wake up, peak about 30 to 60 minutes later (a surge called the cortisol awakening response), then gradually decline to their lowest point around bedtime. That morning spike can be 50 to 150% higher than your waking level, though roughly 15 to 25% of people don’t show this pattern at all.
This rhythm is why doctors order blood draws at specific times. A normal 8 a.m. blood cortisol reading falls between 5 and 25 mcg/dL. That same number at midnight would be a red flag. Every cortisol test is interpreted against the clock, so the time of collection matters as much as the result itself.
Blood Test (Serum Cortisol)
A standard blood draw, usually scheduled first thing in the morning, is the most widely used cortisol test. You’ll have blood taken from a vein in your arm, typically around 8 a.m. when levels should be at or near their daily peak. Results come back quickly, often within a day or two.
Because stress and physical activity both raise cortisol, you may be asked to rest quietly for 15 to 30 minutes before the draw. Let your provider know about any medications you’re taking, especially steroids (including skin creams), hormonal birth control, or anti-seizure drugs, since these can skew results in either direction. A morning value below 5 mcg/dL suggests your adrenal glands may not be producing enough cortisol, while a value well above 25 mcg/dL points toward overproduction.
Saliva Test
Saliva testing is especially useful for checking late-night cortisol, which should be at its lowest point of the day. You collect a sample by placing a small swab or cotton roll in your mouth, usually around 11 p.m. In healthy adults, late-night salivary cortisol stays below about 3.6 nmol/L. Values above that threshold catch roughly 92% of cases of cortisol overproduction. Lowering the cutoff slightly to 2.7 nmol/L raises that detection rate to 97%, which is why many labs use the more sensitive number.
Preparation is straightforward but important: don’t eat, drink, brush your teeth, or floss for at least 30 minutes before collecting the sample. Certain medications, including topical creams, can affect saliva results, so discuss everything you’re using with your provider beforehand. The test is painless and can be done at home, which makes it practical for capturing that bedtime reading without a hospital visit.
24-Hour Urine Test
While blood and saliva give you a snapshot, a 24-hour urine collection captures your total cortisol output over an entire day. You’ll collect every drop of urine into a large container over a full 24-hour period, keeping it refrigerated throughout. Record the exact start and stop times on the lab form, since an incomplete collection will produce misleading results.
Normal values for adults are up to 45 mcg per 24 hours for women and up to 60 mcg per 24 hours for men. This test is particularly helpful when doctors suspect Cushing’s syndrome, because it smooths out the normal fluctuations that can make a single blood or saliva reading hard to interpret. The tradeoff is convenience: carrying a collection jug around for a full day is nobody’s favorite medical experience, but it provides information no other single test can match.
Hair Cortisol
Hair analysis is a newer method that measures cumulative cortisol exposure over weeks or months rather than a single moment. A small section of hair is cut close to the scalp, and each centimeter of length represents roughly one month of cortisol secretion, covering up to about six months (beyond which cortisol in the hair shaft starts to degrade). This makes it uniquely suited for assessing long-term, chronic stress patterns that a blood draw would miss entirely.
The limitation is that standardized reference ranges haven’t been firmly established yet, so results are harder to interpret in a clinical setting. Hair cortisol is more commonly used in research than in routine medical care, but it’s increasingly available through specialty labs.
Stimulation and Suppression Tests
When basic tests show abnormal cortisol but the cause isn’t clear, doctors use challenge tests that push the system in a specific direction and measure how it responds.
ACTH Stimulation Test
This test checks whether your adrenal glands can respond to a signal to produce cortisol. You receive an injection of synthetic ACTH (the hormone that normally tells the adrenals to release cortisol), then have your blood drawn 30 and 60 minutes later. A healthy response means cortisol rises by at least 7 to 10 mcg/dL from baseline and reaches at least 18 mcg/dL by the 60-minute mark. If cortisol barely moves after the injection, it suggests the adrenal glands themselves aren’t working properly, pointing toward adrenal insufficiency.
Dexamethasone Suppression Test
This test works in the opposite direction. You take a pill containing a synthetic steroid (dexamethasone) that should signal your brain to stop asking for cortisol. In the most common overnight version, you swallow a 1 mg pill at 11 p.m. and have blood drawn at 8 a.m. the next morning. If your system is working normally, the morning cortisol will be suppressed to a low level. If it stays high despite the medication, something is overriding the normal feedback loop, which is a hallmark of Cushing’s syndrome.
A higher-dose version (8 mg at 11 p.m.) helps distinguish between different causes of cortisol overproduction once an abnormality has already been confirmed. There are also extended versions of both tests that involve taking smaller doses every six hours for 48 hours, which can provide more detailed information in complex cases.
At-Home Cortisol Kits
Several companies sell saliva-based cortisol kits you can order online and complete at home. These typically involve collecting saliva samples at multiple points during the day, then mailing them to a lab. The concept is sound, since saliva cortisol is a legitimate clinical measurement, but accuracy depends heavily on how carefully you collect and handle the samples. Errors during collection or delays in shipping can produce false results.
Testing at a doctor’s office or hospital is generally more accurate than a self-collected kit. If you do use a home test, treat the results as a starting point for a conversation with your provider rather than a definitive answer. A concerning home result should always be followed up with clinical testing, and a normal result doesn’t necessarily rule out a problem if your symptoms are significant.
How To Prepare for Accurate Results
Regardless of the test type, a few preparation steps apply broadly. Avoid vigorous exercise in the hours before any cortisol test, since physical exertion raises levels. Try to minimize stress on the day of testing (easier said than done, but even sitting quietly for 15 minutes before a blood draw helps). Report all medications to your provider, paying special attention to any form of steroid: oral pills, inhalers, nasal sprays, joint injections, and skin creams all introduce synthetic cortisol that can distort results.
For saliva tests specifically, the 30-minute window of no eating, drinking, or oral care before collection is critical. For 24-hour urine, the most common source of error is forgetting to collect a sample or not refrigerating the container. Set a reminder, and keep the container cold throughout the collection period. Small details in preparation make the difference between a result your doctor can trust and one that needs to be repeated.