Cortisol is tested through blood, saliva, or urine samples, and the right method depends on what your doctor is looking for. A single blood draw is the most common starting point, but saliva and 24-hour urine collections each capture cortisol differently and are often used alongside blood tests to build a fuller picture. Here’s what each test involves and how to prepare.
Why Timing Matters for Every Cortisol Test
Cortisol follows a predictable daily rhythm. Levels peak early in the morning, usually around 6 to 8 a.m., then gradually decline throughout the day until they hit their lowest point late at night. By evening, cortisol typically drops to about half of its morning value. This natural swing is so significant that a “normal” reading at 8 a.m. would look abnormally high at midnight.
Because of this rhythm, every cortisol test is designed around specific collection windows. A result only makes sense when interpreted against the time of day the sample was taken. If your levels don’t follow this expected pattern, that itself can be a diagnostic clue.
Blood Cortisol Test
A standard blood cortisol test is a simple draw at a lab, usually scheduled for 8 a.m. when levels are at their daily peak. In many cases, a second draw is taken around 4 p.m. to see whether your cortisol drops as expected. Comparing those two values gives your doctor a snapshot of your body’s diurnal rhythm. If morning cortisol is unusually low, it may point toward adrenal insufficiency. If evening cortisol stays stubbornly high, it could suggest excess cortisol production.
Most cortisol in your blood is bound to proteins, with only a small fraction circulating freely. Blood tests typically measure total cortisol (both bound and free), which means anything that changes your protein levels, like pregnancy or estrogen-based birth control, can shift results without reflecting a true cortisol problem.
Saliva Cortisol Test
Late-night salivary cortisol testing has become one of the most practical screening tools because it’s painless and can be done at home. You collect a saliva sample, usually between 11 p.m. and midnight, by placing a small swab or cotton roll in your mouth for a few minutes. Saliva measures only the free, unbound cortisol circulating in your system, which makes it less susceptible to the protein-binding issues that can affect blood tests.
The logic behind the late-night timing is straightforward: cortisol should be at its lowest point near midnight. If your saliva sample shows elevated cortisol at that hour, it suggests your body isn’t following its normal shutdown pattern, which is one of the earliest signs of cortisol excess. Home collection kits are widely available, though the accuracy of consumer-grade kits can vary. Kits ordered through a doctor and processed by a certified lab generally produce more reliable results than direct-to-consumer wellness panels.
24-Hour Urine Cortisol Test
A 24-hour urinary free cortisol test measures the total amount of cortisol your body excretes over a full day, smoothing out the peaks and valleys of the daily rhythm. It’s particularly useful for detecting sustained overproduction because it captures cumulative output rather than a single moment.
The collection process requires some planning. You start by urinating at 8 a.m. and discarding that first sample. From that point forward, you collect every bit of urine for the next 24 hours into a provided plastic container, including the final sample at 8 a.m. the next morning. The container can be stored at room temperature or refrigerated. You’ll need to record the total volume before sending or bringing it to the lab. Missing even one bathroom trip during the collection window can throw off the results, so most doctors recommend staying home for the day if possible.
Specialized Suppression and Stimulation Tests
When screening tests come back abnormal, your doctor may order a more targeted test to pinpoint the problem. The two most common are designed to push your cortisol system in opposite directions and see how it responds.
Dexamethasone Suppression Test
This test checks whether your body can properly dial down cortisol production when it receives a signal to do so. You take a small pill (a synthetic steroid) at 11 p.m., then have your blood drawn the next morning at 8 a.m. In a healthy system, that pill tells the brain to stop signaling for more cortisol, and morning levels drop below 1.8 mcg/dL. If cortisol stays elevated despite the suppression signal, it suggests the feedback loop is broken, which is a hallmark of conditions like Cushing’s syndrome.
ACTH Stimulation Test
This test works in the opposite direction. Instead of suppressing cortisol, it stimulates the adrenal glands directly to see if they can ramp up production on demand. A synthetic version of the hormone that normally tells your adrenals to produce cortisol is injected, and blood is drawn 30 to 60 minutes later. A healthy response pushes cortisol above 15 to 16 mcg/dL. If your adrenals can’t hit that threshold, it points toward adrenal insufficiency, meaning the glands aren’t producing enough cortisol on their own.
Hair Cortisol Testing
Hair cortisol analysis is a newer method that captures a much longer window of cortisol exposure. Hair grows at roughly 1 centimeter per month, so a 3-centimeter sample cut closest to the scalp reflects approximately three months of cortisol output. This makes it fundamentally different from blood, saliva, or urine tests, which all measure cortisol over hours to a single day.
The appeal is obvious for anyone trying to assess chronic stress patterns rather than a single-day snapshot. However, hair cortisol is not yet a standard clinical diagnostic tool. It’s used more in research settings and as a complement to traditional tests. Factors like hair treatments, color, and washing frequency can also affect results, so it hasn’t replaced the established methods for diagnosing specific cortisol disorders.
What Can Skew Your Results
Several medications and lifestyle factors can push cortisol readings up or down in ways that mimic real disorders. Being aware of these before testing helps ensure your results reflect what’s actually happening in your body.
- Steroid medications: Any form of glucocorticoid, whether a pill, inhaler, cream, or injection, can interfere with cortisol test interpretation. Even topical steroids applied to the skin may register enough to confuse results.
- Estrogen and oral contraceptives: Estrogen raises the protein that binds cortisol in the blood, which can inflate total cortisol readings on a blood test without actually changing how much free cortisol is active in your body.
- Opioid painkillers: Regular use of opioids, especially long-acting formulations, can lower cortisol levels and produce results that look like adrenal insufficiency.
- Alcohol: Heavy drinking is well known to raise cortisol levels and can trigger falsely positive results on tests used to diagnose cortisol excess.
Physical and emotional stress on the day of testing can also spike cortisol temporarily. If you’re acutely ill, sleep-deprived, or had an unusually stressful morning, your results may not represent your baseline. Tell your doctor about any medications, supplements, or unusual circumstances before the test so they can factor those into the interpretation, or reschedule if needed.
Which Test You’re Likely to Get First
For most people, initial screening starts with one or two of the simpler tests: a morning blood draw, a late-night saliva sample, or a 24-hour urine collection. Your doctor chooses based on what they suspect. If high cortisol is the concern (fatigue, weight gain, high blood sugar), a late-night salivary cortisol or the dexamethasone suppression test is a common first step. If low cortisol is the worry (dizziness, unexplained weight loss, chronic fatigue), a morning blood draw or the ACTH stimulation test is more likely.
No single cortisol test is definitive on its own. Results that come back borderline or abnormal are almost always confirmed with a second type of test or a repeat measurement. Cortisol fluctuates enough day to day that one abnormal reading can simply reflect a bad night’s sleep or a stressful morning, not a medical condition.