Diagnosing high cortisol requires specific lab tests, not just a single blood draw. A random blood test for cortisol is actually unreliable because cortisol levels swing dramatically throughout the day. Instead, doctors use a structured sequence: screening tests to confirm cortisol is genuinely elevated, followed by additional tests to pinpoint the cause.
Signs That Prompt Testing
Not everyone with weight gain or fatigue needs cortisol testing. Doctors look for a cluster of symptoms that progress over time, particularly ones that are unusual for your age. High blood pressure or osteoporosis in a young adult, for example, raises more suspicion than those same conditions in someone over 65. In children, the hallmark pattern is gaining weight while simultaneously falling behind on height growth charts.
Certain physical signs are especially telling. Purple or reddish stretch marks wider than 1 cm (about half an inch), particularly on the abdomen, are much more specific to excess cortisol than the pale stretch marks most people get from weight fluctuations. Weakness in the muscles closest to your trunk, like difficulty standing from a chair or climbing stairs without using your arms, is another strong indicator. A round face, a fat pad between the shoulders, easy bruising, and thin skin that tears or heals slowly round out the picture. The more of these features you have, and the more they worsen over time, the stronger the case for testing.
Three First-Line Screening Tests
The Endocrine Society recommends starting with one of three screening tests. Each captures cortisol from a different angle, and none requires a random blood draw at your doctor’s office.
24-Hour Urine Collection
This test measures the total amount of cortisol your kidneys filter over an entire day, smoothing out the normal ups and downs. You collect all urine for 24 hours in a provided container. For adults, normal values fall between 3.5 and 45 micrograms per 24 hours. Results well above that upper limit suggest genuine cortisol excess. Because individual collections can vary, guidelines recommend doing this test at least twice.
Late-Night Salivary Cortisol
Cortisol normally drops to its lowest point late at night. When it stays elevated at bedtime, that’s a red flag. You collect a saliva sample at home between 11 p.m. and midnight using a kit your doctor provides. Normal late-night values should fall below 100 nanograms per deciliter. This test is popular because it’s painless and easy to do at home, and it’s recommended in duplicate as well, meaning two separate nights of collection.
Overnight Dexamethasone Suppression Test
This test checks whether your body’s cortisol production responds normally to a “stop” signal. You take a 1 mg tablet of dexamethasone (a synthetic steroid) between 11 p.m. and midnight, then have your blood drawn the next morning. In a healthy system, that dose tells the brain to stop producing cortisol, and morning levels drop below 2 micrograms per deciliter. If your cortisol stays above that threshold, the feedback loop isn’t working properly, which points toward excess cortisol production.
What Can Skew Your Results
Several medications and conditions can produce false-positive results, meaning your tests look abnormal even though you don’t truly have a cortisol disorder. Certain drugs that slow how your liver processes dexamethasone, including the antifungal itraconazole, the HIV medication ritonavir, and the heart medication diltiazem, can make the suppression test look falsely abnormal. These typically need to be stopped at least two weeks before testing.
A number of conditions can also push cortisol levels up without reflecting a true hormonal disorder. Major depression, heavy alcohol use (and alcohol withdrawal), poorly controlled diabetes, polycystic ovary syndrome, severe obesity, and even intense physical or emotional stress can all raise cortisol enough to trigger abnormal screening results. Doctors call these “pseudo-Cushing’s states” because the lab numbers overlap with genuine Cushing’s syndrome, but the underlying cause is different. Severe kidney disease is another common confounder, specifically for the urine test. If kidney function is impaired, the overnight dexamethasone suppression test is generally a better choice.
Confirming the Results
A single abnormal screening test isn’t enough for a diagnosis. Guidelines recommend following up an abnormal result with a second, different screening test. If you had an abnormal salivary cortisol, for instance, your doctor would likely order a dexamethasone suppression test or a urine collection next. When two different tests both come back abnormal, the likelihood of true cortisol excess is much higher.
In ambiguous cases where results are borderline or conflicting, more specialized tests can help. One combines dexamethasone with an injection of corticotropin-releasing hormone (the brain signal that triggers cortisol production) to see how the system responds. Another option is measuring cortisol in a blood sample drawn at midnight in a hospital setting, since cortisol should be at its lowest then. These aren’t first-line tests, but they help resolve genuine diagnostic uncertainty.
Finding the Source
Once excess cortisol is confirmed biochemically, the next step is figuring out where it’s coming from. This matters because treatment depends entirely on the cause.
The key dividing test is a blood draw measuring ACTH, the hormone the pituitary gland releases to tell the adrenal glands to produce cortisol. Normal morning ACTH levels run between about 7 and 63 picograms per milliliter. In someone with confirmed high cortisol, a suppressed ACTH level points toward a problem in the adrenal glands themselves, such as an adrenal tumor that’s producing cortisol on its own without waiting for instructions from the brain. A normal or elevated ACTH, on the other hand, means something is overproducing ACTH, which in turn drives the adrenals to make too much cortisol. That “something” is most commonly a small pituitary tumor, though rarely it can be a tumor elsewhere in the body.
Imaging comes after the bloodwork points in a direction. If ACTH is suppressed and an adrenal source is suspected, a CT scan of the abdomen is the standard next step. If ACTH is normal or high, suggesting a pituitary source, a contrast-enhanced MRI of the pituitary gland is ordered. When doctors suspect a rare ectopic source (a tumor outside the pituitary producing ACTH), CT scans of the chest and abdomen are used to search for it. The guiding principle is that lab results and imaging should match before any treatment decisions are made.
Tests to Avoid
The Endocrine Society specifically recommends against using a random blood cortisol level or a random ACTH level as a screening tool. Cortisol varies so much hour to hour that a single snapshot is nearly meaningless. Older tests like urinary 17-ketosteroids and the insulin tolerance test are also discouraged. Jumping straight to imaging, such as ordering a pituitary MRI before confirming cortisol excess with lab work, is another common mistake. Pituitary “incidentalomas,” tiny abnormalities that are harmless and have nothing to do with cortisol, show up in roughly 10% of the general population on MRI. Without biochemical confirmation first, an incidental finding can send you down a costly and stressful diagnostic path that leads nowhere.
What the Diagnostic Timeline Looks Like
Expect the process to take weeks to months rather than days. Initial screening requires at least two rounds of testing, sometimes more if results are borderline. If those are abnormal, confirmatory testing adds another round. Then ACTH measurement and imaging follow. Each step typically involves waiting for results, scheduling follow-ups, and sometimes repeating tests. This pace can feel frustrating, but cortisol disorders are genuinely complex. Rushing to a diagnosis based on a single lab value leads to misdiagnosis more often than it speeds up treatment.
If you’re in the early stages, keeping a symptom log with dates and photographs of physical changes (bruising patterns, stretch marks, facial changes) can be helpful context for your endocrinologist. Tracking your weight, blood pressure, and blood sugar over time also provides useful data points that complement the lab work.