High cortisol is tested through three main screening methods: a 24-hour urine collection, a late-night saliva sample, or a blood test after taking a small dose of a medication called dexamethasone. No single test confirms high cortisol on its own. The standard diagnostic approach requires at least two abnormal results, often from different types of tests, before a diagnosis is made.
Which test you get depends on your situation, but understanding how each one works and what can throw off the results helps you prepare and interpret what comes next.
The Three Recommended Screening Tests
The Endocrine Society specifically recommends these initial tests for detecting abnormally high cortisol:
- 24-hour urinary free cortisol (at least two collections)
- Late-night salivary cortisol (two measurements)
- Overnight dexamethasone suppression test
Notably, the guidelines recommend against using a random blood draw for cortisol as a screening tool. Cortisol fluctuates dramatically throughout the day, peaking in the morning and dropping at night, so a single snapshot of your blood level isn’t reliable for diagnosing excess cortisol. Morning blood cortisol is useful in other contexts (like checking for adrenal insufficiency), but it’s not how high cortisol is screened.
24-Hour Urine Collection
This test measures the total amount of cortisol your body filters out over a full day, which smooths out the natural ups and downs. You start by emptying your bladder at 8 a.m. and discarding that sample, then collecting every drop of urine for the next 24 hours into a plastic container, including the final sample at 8 a.m. the following morning.
Normal values for adults range from about 5 to 64 mcg per 24 hours for men and 6 to 42 mcg for women. People with Cushing’s syndrome (the condition caused by chronically high cortisol) usually have levels above 100 mcg per 24 hours, though there’s wide variation and no single cutoff works perfectly for everyone. Because of this variability, you’ll typically be asked to do the collection at least twice.
The test is straightforward but admittedly inconvenient. You need to carry the collection container with you all day, keep it refrigerated, and avoid contaminating it. The upside is that it doesn’t require any medication or precise timing beyond the 24-hour window.
Late-Night Salivary Cortisol
This test takes advantage of the fact that cortisol should be at its lowest point late at night. If your body is producing too much, that nighttime dip disappears. You collect a saliva sample between 11 p.m. and midnight by placing a small cotton swab in your mouth.
A normal result is below 100 ng/dL. If your result comes back at or above that level, you’ll need a second test to confirm it. Two positive late-night salivary cortisol results can be used to confirm Cushing’s syndrome.
Preparation matters here. For 30 minutes before collecting the sample, don’t eat, drink, brush your teeth, floss, smoke, or vape. Any of these can contaminate the sample or affect the reading. Certain medications can also interfere, so your provider may ask you to temporarily stop some prescriptions beforehand.
This is often the most convenient test for patients since you do it at home, and many people find it easier than a 24-hour urine collection.
Dexamethasone Suppression Test
This test checks whether your body’s cortisol production responds normally to a “shut off” signal. Dexamethasone is a synthetic steroid that, in a healthy person, tells the brain to stop stimulating cortisol production. If your cortisol stays high despite that signal, something is overriding the normal feedback loop.
In the overnight version, you take 1 mg of dexamethasone between 11 p.m. and midnight, then have your blood drawn the next morning. A normal response is a cortisol level suppressed below 1.8 mcg/dL. If cortisol remains above that threshold, it suggests your body is producing cortisol independently of normal regulation.
There’s also a longer version where you take a smaller dose (0.5 mg) every six hours for two full days. A normal result on this version is a greater than 50% drop in cortisol. The overnight test is more common for initial screening because it’s simpler.
What Happens After an Abnormal Result
One abnormal test doesn’t mean you have high cortisol. The standard approach is to confirm with a second recommended test of a different type. If you had an abnormal urine collection, for example, your provider might order a late-night salivary test or a dexamethasone suppression test next.
If two different tests both come back abnormal, that’s when testing shifts toward finding the cause, which could involve imaging of the pituitary gland or adrenal glands, along with additional blood work to measure ACTH (the hormone that tells your adrenals to produce cortisol). On the other hand, if two different tests both come back normal, further testing for Cushing’s syndrome is not recommended unless there’s suspicion of a rare cyclical pattern where cortisol spikes intermittently.
What Can Skew Your Results
Before any biochemical testing, your provider should review every medication you’re taking. Glucocorticoid medications, including pills, injections, creams, and even inhalers, are the most common cause of elevated cortisol. If an outside source of steroids is responsible, no further testing is needed.
Beyond medications, several factors can produce falsely elevated results. Physical or emotional stress raises cortisol, so you may be asked to rest before a blood draw. Intense exercise does the same. Oral contraceptives and estrogen therapy increase a protein in your blood that binds cortisol, which can make total cortisol levels appear higher than they actually are on blood tests. Certain anti-seizure medications speed up how quickly your body clears dexamethasone, which can make the suppression test unreliable. In those cases, the guidelines recommend using a urine or saliva test instead.
Testing During Pregnancy
Pregnancy naturally raises cortisol levels significantly, making interpretation tricky. Total cortisol in the blood increases two to three times above normal due to hormonal changes, and by the third trimester, cortisol levels in a healthy pregnant woman can look identical to Cushing’s syndrome levels in a non-pregnant adult. The normal daily rhythm of cortisol also flattens out late in pregnancy.
For this reason, standard reference ranges don’t apply. Third-trimester serum cortisol can reach 12 to 50 mcg/dL, compared to a normal non-pregnant morning range of 7 to 25 mcg/dL. Late-night salivary cortisol and urine cortisol both require trimester-specific cutoffs to be meaningful. The Endocrine Society recommends using urine free cortisol rather than dexamethasone testing when evaluating pregnant patients, since dexamethasone crosses the placenta.
Morning Blood Cortisol: What It Does Tell You
While a standard morning blood draw isn’t recommended for screening high cortisol, it’s still commonly ordered and useful in other scenarios. Morning cortisol (drawn around 8 a.m.) normally falls between 7 and 25 mcg/dL, while afternoon levels (around 4 p.m.) drop to 2 to 14 mcg/dL. This test is most helpful when low cortisol is the concern, such as when evaluating adrenal insufficiency. A morning cortisol below 10 mcg/dL with symptoms of fatigue and weakness warrants further investigation.
If your provider ordered a morning cortisol and it came back elevated, that alone doesn’t confirm a problem. Stress before the blood draw, recent exercise, or simply being anxious about the needle can push the number up. A truly elevated result would prompt one of the three formal screening tests described above.