Several tests are used to check adrenal function, and the right one depends on whether your doctor suspects your adrenal glands are producing too much or too little of a hormone. The most common starting point is a simple morning blood draw to measure cortisol, but the full diagnostic toolkit includes urine collections, saliva samples, stimulation tests, suppression tests, and imaging. Here’s what each test involves and what it’s looking for.
Morning Cortisol Blood Test
Cortisol follows a predictable daily rhythm: it peaks between 6 and 8 a.m. (typically 10 to 20 mcg/dL) and drops to its lowest point around midnight (3 to 10 mcg/dL by 4 p.m.). A morning blood draw takes advantage of that natural peak. If your cortisol comes back below about 5 mcg/dL early in the morning, adrenal insufficiency is likely. If it’s above roughly 12 mcg/dL, insufficiency can usually be ruled out. Values between those two numbers fall into a gray zone that requires further testing.
Because the timing matters so much, you’ll typically be asked to have blood drawn between 6 and 8 a.m. Oral estrogen, including birth control pills, can artificially raise cortisol readings by increasing a protein that carries cortisol in the blood. If you’re taking hydrocortisone or cortisone acetate, your doctor will usually ask you to skip at least 12 hours of doses before the test.
ACTH Stimulation Test
This is the gold standard for diagnosing adrenal insufficiency. It checks whether your adrenal glands can respond when given a signal to produce cortisol. You receive an injection of a synthetic version of ACTH, the pituitary hormone that normally tells your adrenals to ramp up cortisol production. Blood is drawn at baseline, then again at 30 and 60 minutes.
A healthy adrenal response pushes cortisol above about 18 mcg/dL. If your cortisol stays below that threshold, your adrenal glands aren’t producing enough on demand, which points to adrenal insufficiency. The test takes about an hour, and aside from the injection and blood draws, most people find it straightforward. In critically ill patients, doctors sometimes look for a cortisol rise of at least 9 mcg/dL from baseline rather than an absolute number.
Late-Night Salivary Cortisol
Because cortisol should be at its lowest around midnight, an elevated late-night level is one of the earliest signs of Cushing’s syndrome, a condition caused by too much cortisol. This test is simple: you collect a saliva sample at home late at night by chewing on a small cotton swab. No needles, no lab visit.
International guidelines recommend this test as a first-line screen for Cushing’s. Normal late-night salivary cortisol falls below about 1 mcg/L. Levels above roughly 1.15 to 1.30 mcg/L raise suspicion for excess cortisol production. Doctors often ask you to repeat the test on two separate nights, since a single elevated reading isn’t enough to confirm a diagnosis.
24-Hour Urine Cortisol
Rather than capturing cortisol at a single moment, this test measures your total cortisol output over an entire day. You collect every drop of urine for 24 hours in a special container that you keep refrigerated. The clock starts after your first morning bathroom trip (which you don’t collect) and ends with a final collection exactly 24 hours later.
High values suggest Cushing’s syndrome. The test is useful because it smooths out the normal ups and downs of cortisol throughout the day, giving a more complete picture of overall production. The inconvenience of carrying a jug around for a day is the main drawback, but the information it provides is hard to get any other way.
Dexamethasone Suppression Test
This test checks whether your body’s cortisol production can be turned down by an outside signal. Dexamethasone is a synthetic steroid that, in a healthy system, tells the brain to stop asking the adrenals for more cortisol. If cortisol stays high despite that signal, something is overriding the normal feedback loop.
The overnight version is the simplest: you take a 1 mg tablet at 11 p.m. and have blood drawn at 8 a.m. the next morning. If your morning cortisol drops below 1.8 mcg/dL, Cushing’s syndrome is effectively ruled out. If it doesn’t suppress, further testing is needed. A longer two-day version using smaller doses every six hours provides similar information with slightly different cutoffs.
There’s also a high-dose version used after Cushing’s has already been confirmed, which helps pinpoint the cause. In that version, you take 8 mg at 11 p.m. If cortisol drops by more than 50% the next morning, the problem is likely in the pituitary gland rather than the adrenal gland itself. Estrogen and oral contraceptives can interfere with this test, so your doctor may ask you to stop them beforehand.
Aldosterone and Renin Levels
Your adrenal glands don’t just make cortisol. They also produce aldosterone, a hormone that controls blood pressure by regulating sodium and potassium. When a doctor suspects primary aldosteronism (a common cause of hard-to-control high blood pressure), they’ll order a blood test measuring both aldosterone and renin, then calculate the ratio between them.
In primary aldosteronism, aldosterone is high while renin is suppressed, producing an elevated ratio. If the ratio is high, confirmatory testing follows, often involving salt loading or saline infusion to see whether aldosterone appropriately decreases. Certain blood pressure medications, particularly diuretics, can skew results, so your doctor may switch or pause medications for a few weeks before testing.
Plasma Metanephrines
The inner part of the adrenal gland (the medulla) produces adrenaline and related hormones. A rare tumor called a pheochromocytoma can cause this region to overproduce, leading to episodes of high blood pressure, rapid heart rate, sweating, and headaches. The best screening test is a blood draw for plasma free metanephrines, which are breakdown products of adrenaline.
This test catches 99% of pheochromocytomas, compared to about 86% for the older method of collecting 24-hour urine catecholamines. The tradeoff is that plasma metanephrines sometimes flag false positives, with a specificity of about 89%. If levels come back elevated, the next step is usually imaging to locate the tumor.
DHEA-S Blood Test
DHEA-S is an androgen (a type of hormone involved in male-pattern characteristics) produced almost entirely by the adrenal glands. Testing it helps evaluate conditions like congenital adrenal hyperplasia, adrenal tumors, and adrenal insufficiency. Elevated DHEA-S can point to certain forms of congenital adrenal hyperplasia or androgen-producing adrenal tumors, while low levels show up in adrenal insufficiency and, somewhat counterintuitively, in some adrenal tumors as well.
When DHEA-S is high and an adrenal tumor is present, it also serves as a useful marker for monitoring after surgery. If levels drop post-operatively and then rise again, it can signal recurrence.
Adrenal Imaging
Once blood or urine tests point to an adrenal problem, imaging helps identify structural causes like tumors or enlarged glands. CT scans are the most common first step. On a CT without contrast, a reading of 10 Hounsfield units or less strongly suggests a benign, fat-rich adenoma, with 98% specificity. About 30% of adenomas are “lipid-poor” and measure above 10 HU, which can make them harder to distinguish from something more concerning.
Pheochromocytomas typically measure 40 to 50 HU on unenhanced CT, while very high values above 150 HU raise stronger suspicion. Adrenal cancers tend to look irregular and uneven, with areas of bleeding or dead tissue. MRI adds detail in ambiguous cases, since different tumor types have characteristic signal patterns. Nodules larger than 4 cm generally warrant surgical removal regardless of hormonal activity, because the risk of malignancy increases with size.
How Doctors Decide Which Tests to Order
The choice of test depends on the clinical question. If you’re being evaluated for fatigue, low blood pressure, or unexplained weight loss, your doctor is likely screening for adrenal insufficiency and will start with a morning cortisol, possibly followed by an ACTH stimulation test. If the concern is weight gain, high blood pressure, easy bruising, or a rounded face, the workup shifts toward Cushing’s syndrome with salivary cortisol, urine cortisol, or a dexamethasone suppression test. Episodes of sudden high blood pressure with sweating and pounding heartbeat trigger testing for pheochromocytoma via plasma metanephrines.
Most people won’t need every test on this list. Testing typically moves in steps: a screening test first, then confirmatory testing if the initial result is abnormal, then imaging if a structural problem is suspected. The process can take a few weeks from start to finish, partly because some tests need to be repeated and partly because medications sometimes need to be paused before accurate results can be obtained.