High cortisol is tested through three main methods: a late-night saliva sample, a 24-hour urine collection, or a blood test after taking a small dose of a steroid pill called dexamethasone. Endocrinologists typically require abnormal results on at least two separate tests before confirming a diagnosis, because cortisol fluctuates throughout the day and can spike temporarily from stress, illness, or alcohol use.
Why Cortisol Testing Isn’t Straightforward
Cortisol follows a natural daily rhythm. It peaks in the early morning, with normal blood levels between 10 and 20 mcg/dL around 6 to 8 a.m., then drops to 3 to 10 mcg/dL by 4 p.m. and falls even lower at night. A single random blood draw can’t tell you much, because the number depends heavily on what time it was taken and what was happening in your body that day. The Endocrine Society specifically recommends against using a random blood cortisol level to screen for high cortisol.
Several things can push cortisol readings higher without reflecting a true hormonal problem. Heavy alcohol use is well known to raise cortisol and produce falsely positive results. Any form of glucocorticoid medication (steroid creams, inhalers, pills, or injections) can also skew results. Your doctor will typically review your full medication list before ordering any cortisol tests to rule out these external sources first.
Late-Night Salivary Cortisol Test
This is one of the most convenient screening tests because you do it at home. The idea is simple: cortisol should be at its lowest point late at night. If it’s still elevated, that’s a red flag. You collect a saliva sample, usually between 11 p.m. and 1 a.m., using a swab or by spitting into a tube provided in a kit.
Preparation matters. You should avoid eating for 60 minutes before collection, skip alcohol for at least 12 hours beforehand, and avoid brushing or flossing your teeth (anything that could cause your gums to bleed). About 10 minutes before collecting, rinse your mouth thoroughly with water. A result above 145 ng/dL (4 nmol/liter) suggests cortisol is abnormally high.
Salivary cortisol testing has strong clinical support. A 2005 study in Clinical Endocrinology found that salivary cortisol measured by enzyme immunoassay is actually preferable to blood cortisol for assessing how the stress hormone system is functioning. The Endocrine Society recommends collecting two separate late-night samples, not just one, to confirm the pattern.
24-Hour Urine Free Cortisol
This test measures your total cortisol output over an entire day, which smooths out the natural peaks and dips. You’ll be given a large collection container and asked to save every urine sample for a full 24-hour period. The container needs to be kept refrigerated (or contain a preservative) during collection, and you’ll need to record the total volume before sending it to the lab.
The main advantage of this test is that it captures the big picture rather than a single snapshot. A result above the lab’s normal reference range suggests excess cortisol production. Like the saliva test, the Endocrine Society recommends at least two separate collections to increase reliability. The downside is obvious: carrying around a collection jug for a full day is inconvenient, and missing even one sample during the 24 hours can throw off the results.
Dexamethasone Suppression Test
This test checks whether your body’s cortisol regulation is working properly. Dexamethasone is a synthetic steroid that, in a healthy system, signals the brain to stop producing cortisol. You take a small pill (1 mg) at bedtime, then have your blood drawn the next morning. If your cortisol drops below 1.8 mcg/dL, the system is responding normally. If it stays above that threshold, cortisol production may be running unchecked.
There’s a longer version of this test where you take 2 mg per day for 48 hours, but the overnight version is more commonly used for initial screening. One important caveat: this test isn’t perfect on its own. Research published in the Journal of Clinical Endocrinology & Metabolism found that about 18% of patients with confirmed Cushing’s disease (the most common cause of excess cortisol) still managed to suppress their cortisol below 5 mcg/dL on this test, and 8% suppressed below 2 mcg/dL. In other words, some people with genuinely high cortisol can pass this test, particularly those with milder cases. That’s why no single test is used alone to rule the condition in or out.
How Doctors Interpret the Results
The diagnostic process follows a clear pattern. Your doctor will start with one of the three screening tests above, chosen based on your situation. If that first result comes back abnormal, you’ll take a different type of test to confirm. Two abnormal results from two different tests is the threshold for moving forward with a diagnosis.
If two different tests both come back normal, high cortisol is effectively ruled out (with a rare exception for cyclical cases where cortisol spikes intermittently). If results are mixed, with one test abnormal and another normal, further evaluation is needed to sort out whether the abnormal result was a false positive from stress, medication, or alcohol.
Once excess cortisol is confirmed, the next step is figuring out where it’s coming from. This might involve additional blood tests measuring ACTH (the hormone that tells your adrenal glands to produce cortisol) or a specialized procedure called inferior petrosal sinus sampling, where blood is drawn from veins near the pituitary gland to determine whether a small tumor there is driving the overproduction.
Who Should Be Tested
Cortisol testing isn’t recommended as a general screening tool. The Endocrine Society guidelines identify specific groups where testing makes sense:
- People with features unusual for their age, such as osteoporosis or high blood pressure developing earlier than expected
- People with multiple worsening symptoms, particularly the classic combination of weight gain (especially in the face and midsection), thinning skin, easy bruising, and purple stretch marks
- Children whose height percentile is dropping while their weight percentile is climbing
- People with an adrenal mass found incidentally on imaging done for another reason
At-Home Kits vs. Lab-Ordered Tests
Consumer saliva kits for cortisol are widely available online, and the underlying science is sound. Saliva testing for cortisol is considered reliable and well-validated compared to blood testing. However, a home kit result on its own won’t get you a diagnosis. Clinical guidelines require at least two abnormal results from validated tests, and the interpretation depends on knowing exactly when the sample was collected, what medications you’re taking, and whether collection instructions were followed precisely.
A home kit can be a reasonable starting point if you’re curious and want data before scheduling an appointment. But if you’re experiencing symptoms that concern you, getting tested through a doctor ensures the results are processed by a certified lab, timed correctly, and interpreted alongside your medical history. It also means you can move directly to confirmatory testing if the first result is abnormal, rather than starting the process over.