A cortisol test measures how much cortisol, your body’s primary stress hormone, is circulating in your system. It can use blood, urine, or saliva, and it’s typically ordered when a doctor suspects your adrenal glands are producing too much or too little cortisol. Normal morning blood cortisol falls between 10 and 20 micrograms per deciliter (mcg/dL), dropping to 3 to 10 mcg/dL by late afternoon.
Why Cortisol Levels Matter
Cortisol does far more than respond to stress. It regulates blood sugar, controls inflammation, influences blood pressure, and helps your body convert food into energy. Your adrenal glands, which sit on top of your kidneys, produce cortisol on a daily rhythm: levels peak between 6 and 8 a.m. to help you wake up, then gradually decline through the day, reaching their lowest point around midnight.
When this system breaks down, either producing too much or too little cortisol, the effects show up across your entire body. Excess cortisol over time can cause rapid weight gain (especially around the midsection and face), thinning skin that bruises easily, muscle weakness, and high blood sugar. This pattern points toward Cushing syndrome. Too little cortisol causes the opposite problem: fatigue, unintentional weight loss, low blood pressure, darkening skin, and dizziness. That pattern suggests adrenal insufficiency, sometimes called Addison’s disease.
Three Types of Cortisol Tests
Blood (Serum) Test
This is the most common version. A technician draws blood from a vein, usually twice in one day: once in the early morning when cortisol should be at its highest, and again around 4 p.m. when it should be significantly lower. Comparing these two readings shows whether your cortisol follows its expected daily rhythm. A morning value well below 10 mcg/dL or an afternoon value that stays elevated can both signal a problem.
24-Hour Urine Test
Instead of capturing a single moment, this test measures your total cortisol output over a full day. You’ll collect every urine sample over 24 hours in a special container provided by the lab. It’s less convenient than a blood draw, but it smooths out the natural ups and downs and gives a reliable picture of your overall cortisol production. Doctors often use it when screening for Cushing syndrome, where a result above the normal range for the lab’s specific assay raises concern.
Late-Night Saliva Test
This one you can do at home. You collect a saliva sample using a kit, typically between 11 p.m. and 1 a.m. The timing matters because cortisol should be at its lowest point late at night. If it’s still elevated, that’s a red flag. In healthy people, bedtime salivary cortisol generally stays below 145 nanograms per deciliter. Values above that threshold suggest the body isn’t following its normal cortisol cycle, which is one of the hallmarks of Cushing syndrome. Your doctor may ask you to collect multiple samples at different times to map your cortisol pattern across the day.
Specialized Suppression and Stimulation Tests
Sometimes a basic cortisol measurement isn’t enough to make a diagnosis, and your doctor needs to see how your system responds to a challenge.
The dexamethasone suppression test checks whether your body can “turn down” cortisol production on command. You take a small dose of a synthetic steroid pill (usually at bedtime), and your blood cortisol is measured the next morning. In a healthy system, the pill signals the brain to stop asking the adrenal glands for cortisol, so levels drop. If your morning cortisol stays above 1.8 mcg/dL after taking the pill, that suggests something is overriding the normal off-switch. At that cutoff, the test catches over 95% of Cushing syndrome cases, though some people without the condition will also test positive. A higher cutoff of 5 mcg/dL is more specific but misses more true cases.
The ACTH stimulation test works in the opposite direction, checking whether your adrenal glands can ramp up production. You receive an injection of synthetic ACTH, the hormone that normally tells your adrenals to produce cortisol. Blood is drawn before the injection and again 30 or 60 minutes later. Healthy adrenal glands respond with a clear rise in cortisol. In people with Addison’s disease or long-standing adrenal insufficiency, cortisol barely budges because the adrenal glands are too damaged to respond.
What Can Affect Your Results
Cortisol is sensitive to a wide range of influences, which means your results can be thrown off if certain factors aren’t accounted for. Physical or emotional stress, illness, and intense exercise all raise cortisol temporarily. If you’re stressed or sick on the day of a blood draw, your results may look abnormally high even though your baseline is perfectly normal.
Several categories of medication also shift cortisol levels. Antidepressants and antipsychotic medications tend to lower both baseline cortisol and cortisol measured during suppression tests. Stimulant medications for ADHD tend to raise cortisol or leave it unchanged. Oral contraceptives increase a protein in the blood that binds to cortisol, which can make total cortisol levels appear higher than they actually are on a standard blood test. Any steroid medication, whether a pill, cream, inhaler, or injection, can suppress your body’s own cortisol production and distort results.
Tell your doctor about every medication and supplement you take before the test. In some cases, you may need to pause a medication temporarily, though you should never stop anything without being told to do so.
What Happens After the Results
A single abnormal cortisol reading rarely leads to a diagnosis on its own. Cortisol fluctuates naturally, and one unusual result could reflect a stressful day, a medication interaction, or the timing of your blood draw. Doctors typically confirm abnormal findings by repeating the test or using a different type of cortisol test to cross-check the result. For instance, if your late-night saliva test comes back high, your doctor might follow up with a dexamethasone suppression test or a 24-hour urine collection.
If results consistently point toward excess cortisol, imaging scans of the pituitary gland or adrenal glands may come next to identify the source. If results suggest adrenal insufficiency, additional blood tests measuring ACTH itself help distinguish whether the problem originates in the adrenal glands or in the pituitary gland that controls them. The type of adrenal insufficiency determines the treatment approach, so pinpointing the source matters.
Cortisol testing is straightforward from your perspective, but interpreting the results requires context: the time of day, your medications, your stress level, and which test was used all factor in. That’s why these tests are almost always read as part of a bigger clinical picture rather than in isolation.