Addison’s disease is diagnosed through a combination of blood tests that measure hormone levels, with the key confirmatory test being the cosyntropin stimulation test. Because symptoms like fatigue, weight loss, and low blood pressure overlap with many other conditions, reaching a diagnosis often takes time and involves ruling out other possibilities. Here’s what the process typically looks like from start to finish.
Why Diagnosis Is Often Delayed
The early signs of Addison’s disease, which is also called primary adrenal insufficiency, are frustratingly vague. Fatigue, nausea, muscle weakness, and abdominal pain can point to dozens of conditions. Even the more distinctive clue, darkening of the skin (especially on the knuckles, gums, and skin creases), doesn’t always raise immediate suspicion. Many people see multiple doctors over months or even years before the right tests are ordered.
What often triggers testing is a pattern of symptoms that doesn’t fit a simpler explanation: persistent low blood pressure, salt cravings, unexplained weight loss, or bloodwork that keeps showing low sodium or high potassium. In some cases, the first real clue comes during an emergency when the body can no longer compensate for the missing hormones.
Morning Cortisol and ACTH: The First Blood Tests
The initial screening step is a blood draw taken within three hours of waking, typically between 6 and 9 AM, when cortisol naturally peaks. A morning cortisol level below 5 mcg/dL strongly suggests adrenal insufficiency, while a level at or above 18 mcg/dL makes the diagnosis unlikely. Values that fall between those two numbers sit in a gray zone and require further testing.
ACTH, the hormone your pituitary gland sends to tell your adrenal glands to produce cortisol, is measured at the same time. In Addison’s disease, the adrenal glands are damaged and can’t respond, so the pituitary keeps sending louder and louder signals. The result is a low cortisol paired with a high ACTH. This combination is the hallmark of primary adrenal insufficiency and helps distinguish it from problems originating in the pituitary gland, where both ACTH and cortisol tend to be low together.
The Cosyntropin Stimulation Test
The Endocrine Society considers the cosyntropin stimulation test the gold standard for confirming Addison’s disease. It directly measures whether your adrenal glands can respond to stimulation.
The test works like this: a baseline blood sample is drawn, then you receive an injection of cosyntropin, a synthetic version of ACTH. The standard adult dose is 250 micrograms given intravenously. Blood is drawn again 30 or 60 minutes later to see how your cortisol responded. In a healthy person, cortisol rises sharply. In someone with Addison’s disease, cortisol stays flat or barely budges because the adrenal glands are too damaged to respond. A peak cortisol that remains below 18 mcg/dL after stimulation confirms adrenal insufficiency.
The test takes about an hour and is straightforward from a patient perspective. No fasting is required, and the injection itself causes minimal discomfort. Results are usually available within a day or two.
Electrolyte Patterns That Support the Diagnosis
Routine blood chemistry often reveals a characteristic pattern before anyone suspects Addison’s disease. The adrenal glands produce aldosterone, a hormone that helps your kidneys retain sodium and manage potassium. When the glands fail, aldosterone drops, leading to low sodium (hyponatremia) and high potassium (hyperkalemia), sometimes with a mild acid buildup in the blood.
Interestingly, in the earliest stages of adrenal failure, aldosterone levels and a related marker called renin can become abnormal before cortisol or ACTH levels shift noticeably. Low aldosterone paired with elevated renin can be the first biochemical sign, sometimes appearing months before the full clinical picture develops. This is one reason some doctors check aldosterone and renin levels alongside cortisol when they suspect the condition.
The severity of these electrolyte shifts varies. Some people compensate well for a while because other hormones partially pick up the slack in managing sodium. Others develop significant salt wasting that leads to dehydration, low blood pressure, and eventually crisis.
Diagnosing During an Adrenal Crisis
Some people are first diagnosed with Addison’s disease in an emergency room during an adrenal crisis. This is a life-threatening situation where the body’s cortisol supply is so depleted that blood pressure drops dangerously, often failing to respond to standard treatments.
The clinical clues that point toward adrenal crisis include blood pressure that drops far out of proportion to the illness, low blood sugar, low sodium, high potassium, fever, vomiting, and severe dehydration. In this situation, treatment starts immediately with high-dose hydrocortisone before test results come back. A blood sample is typically drawn for cortisol and ACTH before the first dose so the numbers aren’t affected, but confirming the diagnosis through a formal stimulation test can wait until the patient is stable. A cortisol level below 18 mcg/dL during acute illness, when cortisol should be elevated from stress, is highly suggestive.
Finding the Underlying Cause
Once adrenal insufficiency is confirmed, the next step is figuring out why the adrenal glands failed. The most common cause in adults is autoimmune destruction, where the immune system gradually attacks the adrenal cortex. This accounts for roughly 80 to 90 percent of cases in developed countries.
The key test here is a blood test for antibodies against an enzyme called 21-hydroxylase. These antibodies are detectable in about 90% of people with autoimmune Addison’s disease, particularly when measured close to the time of diagnosis. They are absent in other forms of adrenal insufficiency, which makes them a reliable way to confirm the autoimmune cause. If you test positive, your doctor will likely screen for other autoimmune conditions that commonly occur alongside Addison’s, such as thyroid disease or type 1 diabetes.
If 21-hydroxylase antibodies come back negative, other causes need to be considered. In men with negative antibody results, testing for a genetic condition called adrenoleukodystrophy is recommended. Infections like tuberculosis and fungal diseases are important causes in parts of the world where those infections are more common.
Imaging the Adrenal Glands
A CT scan of the abdomen can help identify the cause when antibody testing is inconclusive. What the adrenal glands look like on the scan tells a different story depending on the underlying process. In autoimmune Addison’s disease, the glands are typically shrunken (atrophic) because the immune system has gradually destroyed the tissue. In tuberculosis or fungal infections, the glands are often enlarged, and calcium deposits may be visible in both glands. Enlarged glands can also indicate hemorrhage, infiltrating cancers, or other inflammatory conditions.
Distinguishing Primary From Secondary Adrenal Insufficiency
Not all adrenal insufficiency is Addison’s disease. Addison’s specifically refers to failure of the adrenal glands themselves (primary). But the adrenals can also underperform because the pituitary gland isn’t sending enough ACTH to stimulate them (secondary), or because someone has been on long-term corticosteroid medications that suppressed the system.
The ACTH level drawn alongside morning cortisol is the main tool for separating these. A high ACTH with low cortisol points to primary disease: the pituitary is working hard, but the adrenals can’t respond. A low or inappropriately normal ACTH with low cortisol points to a pituitary or hypothalamic problem. This distinction matters because the treatment approach and the search for an underlying cause take different paths. People with primary adrenal insufficiency typically need both cortisol and aldosterone replacement, while those with secondary insufficiency usually only need cortisol since their aldosterone production remains intact.
If a pituitary problem is suspected, an MRI of the brain is often the next step to look for tumors, inflammation, or other structural issues affecting the gland.