Checking adrenal function typically starts with a simple morning blood draw to measure cortisol, then moves to more specialized tests depending on whether your doctor suspects your adrenal glands are producing too little or too much hormone. The specific test depends on the suspected problem: a stimulation test for underactive adrenals, a suppression test for overactive ones, and additional hormone panels to round out the picture.
Morning Cortisol: The First Step
The most common starting point is a blood test for cortisol drawn around 8 or 9 AM, when levels naturally peak. This single measurement can sometimes confirm or rule out a problem without further testing. A morning cortisol below about 100 nmol/L (roughly 3.6 µg/dL) strongly suggests adrenal insufficiency, with some studies showing 98% to 100% specificity at that threshold. On the other end, a level above 450 nmol/L (about 16 µg/dL) generally rules out insufficiency.
The gray zone between those numbers is where things get tricky. If your result falls in that range, your doctor will order a stimulation test to get a clearer answer. The Endocrine Society recommends using a cutoff of 140 nmol/L (about 5 µg/dL) alongside an ACTH level as an initial screen. ACTH is the pituitary hormone that tells your adrenal glands to produce cortisol, and measuring both together helps pinpoint whether the problem originates in the adrenal glands themselves or in the brain’s signaling.
The ACTH Stimulation Test
This is considered the gold standard for diagnosing adrenal insufficiency. The concept is straightforward: your doctor gives you a synthetic version of ACTH (the hormone that normally stimulates your adrenals) and then checks whether your adrenal glands respond appropriately.
Here’s what happens during the test. A baseline blood sample is drawn, then you receive an injection of synthetic ACTH. Blood is drawn again at 30 minutes and 60 minutes. The whole process takes about an hour. A normal response means your cortisol rises above 500 to 600 nmol/L (roughly 18 to 22 µg/dL). If your adrenals can’t reach that level even with direct stimulation, that confirms they aren’t functioning properly.
You don’t need to fast for this test, but timing still matters. It’s typically done in the morning. If you’re taking any steroid medications, including hydrocortisone, prednisone, or even steroid inhalers or skin creams, let your doctor know. External steroids can suppress your adrenal glands and affect results. Oral contraceptives can also raise cortisol-binding proteins in the blood, which artificially inflates total cortisol readings.
Tests for Overactive Adrenals
If the concern is too much cortisol (Cushing syndrome), the testing approach flips. Instead of stimulating the adrenals, these tests check whether cortisol production can be properly suppressed or whether it stays inappropriately high.
Overnight Dexamethasone Suppression Test
You take a 1 mg tablet of dexamethasone (a synthetic steroid) between 11 PM and midnight. The next morning, your blood is drawn for cortisol. In a healthy person, the dexamethasone signals the brain to stop telling the adrenals to produce cortisol, so the morning level drops. If your cortisol comes back below 1.8 µg/dL (50 nmol/L), Cushing syndrome is effectively ruled out. That cutoff gives the test about 95% sensitivity, meaning it catches the vast majority of true cases.
Late-Night Salivary Cortisol
Cortisol normally drops to its lowest point around midnight. In Cushing syndrome, it stays elevated. You collect a saliva sample at home before bed, typically between 11 PM and midnight, using a kit your doctor provides. This test is convenient because it doesn’t require a blood draw or a hospital visit. For the most common form of Cushing syndrome (driven by excess pituitary signaling), salivary cortisol testing is highly sensitive, catching about 97% of cases in one study. It’s less reliable for Cushing syndrome caused by adrenal tumors directly, where sensitivity drops to around 30%, so it’s usually combined with other screening methods.
24-Hour Urine Cortisol
This test measures how much free cortisol your body excretes over a full day, smoothing out the natural ups and downs that make a single blood draw less reliable. You collect all urine produced in a 24-hour period in a special container. For adults, the normal range is 3.5 to 45 µg per 24 hours. Values consistently above that range point toward Cushing syndrome. Mayo Clinic Labs considers this the preferred screening test for the condition.
Checking Aldosterone and Renin
Your adrenal glands don’t just make cortisol. They also produce aldosterone, which controls blood pressure by regulating sodium and potassium balance. If you have resistant high blood pressure (the kind that doesn’t respond well to medication), your doctor may check for primary aldosteronism, a condition where the adrenals overproduce aldosterone.
The screening test is the aldosterone-to-renin ratio (ARR). Both hormones are measured from a single blood draw, ideally taken in the morning after you’ve been upright for at least two hours. Current guidelines use a cutoff of 2.4 for people under 50, and 3.7 for those 50 and older. A positive screen doesn’t confirm the diagnosis on its own; it flags the need for a confirmatory test, which usually involves salt loading to see if aldosterone levels stay elevated when they should suppress. Certain blood pressure medications, particularly spironolactone and some diuretics, can interfere with results and may need to be paused before testing.
DHEA-S: Adrenal Androgen Levels
DHEA-S is a hormone produced almost exclusively by the adrenal glands. Measuring it helps assess adrenal androgen output, which matters in conditions like congenital adrenal hyperplasia, adrenal tumors, or unexplained symptoms like unusual hair growth or acne in women. It’s a simple blood test with no special preparation needed.
Normal ranges vary significantly by age and sex. For women aged 18 to 29, the typical range is 45 to 320 µg/dL, declining steadily to under 145 µg/dL after age 59. For men, the range starts higher (110 to 510 µg/dL at ages 18 to 29) and also decreases with age. Levels that are abnormally high or low for your age and sex prompt further investigation into what’s driving the imbalance.
Adrenal Imaging
When blood and urine tests reveal a hormonal abnormality, imaging helps locate the cause. CT scanning is the primary tool for evaluating the adrenal glands. One of its most useful features is the ability to measure tissue density in Hounsfield units, which helps distinguish harmless growths from concerning ones.
About 70% of adrenal adenomas (benign tumors) are lipid-rich, meaning they contain enough fat to measure below 10 Hounsfield units on an unenhanced CT scan. That low density is a strong indicator the growth is benign. Metastatic tumors and adrenal cancers typically measure above 10 Hounsfield units and often appear larger and more irregular. Myelolipomas, another benign type, are even more fat-dense, often below negative 50 Hounsfield units. Adrenal cysts show density close to water.
MRI is used when CT results are inconclusive or when radiation exposure needs to be minimized. It’s particularly useful for characterizing lipid-poor adenomas, the 30% of benign tumors that don’t contain enough fat to be identified by CT density alone.
Preparing for Adrenal Testing
Several common medications can distort adrenal test results. Corticosteroids are the biggest concern. Even topical creams, nasal sprays, and inhaled steroids can suppress the body’s natural cortisol production over time, leading to falsely low results on stimulation testing. Oral contraceptives increase cortisol-binding proteins, which raises total cortisol readings without actually changing the amount of active hormone in your body. For aldosterone testing, diuretics, ACE inhibitors, and certain other blood pressure medications affect the aldosterone-renin balance and may need to be switched or paused weeks before the test.
Timing and conditions matter too. Morning cortisol tests should be drawn between 7 and 9 AM. Physical stress, illness, and sleep deprivation all raise cortisol independently, so testing during an acute illness can give misleadingly high readings. For salivary cortisol, you’ll need to avoid eating, drinking, or brushing your teeth for a period before collecting the sample. Your doctor’s office will give you specific instructions for each test, but the single most important thing you can do is provide a complete list of every medication and supplement you’re taking, including anything applied to the skin or inhaled.