What tests are used to diagnose adrenal insufficiency?

Diagnostic Tests to Rule Out Adrenal Insufficiency

The cosyntropin (ACTH) stimulation test with cortisol measurements at baseline, 30 minutes, and 60 minutes post-administration is the gold standard test to definitively rule out adrenal insufficiency, with a peak cortisol >500-550 nmol/L (>18-20 mcg/dL) excluding the diagnosis. 1, 2, 3

Initial Screening Tests

Morning (8 AM) serum cortisol and plasma ACTH measurements are the first-line screening tests that should be obtained simultaneously to assess the hypothalamic-pituitary-adrenal axis. 1, 3, 4

Interpretation of Morning Cortisol Levels:

• Cortisol >13 mcg/dL (>350 nmol/L) reliably rules out adrenal insufficiency in most cases 5, 6
• Cortisol <5 mcg/dL (<140 nmol/L) with elevated ACTH is diagnostic of primary adrenal insufficiency 1, 3, 4
• Cortisol 5-10 mcg/dL (140-275 nmol/L) requires confirmatory testing with cosyntropin stimulation test 1, 3
• Cortisol <9 mcg/dL (<250 nmol/L) with elevated ACTH in acute illness is diagnostic of primary adrenal insufficiency 1

ACTH Interpretation:

• High ACTH with low cortisol indicates primary adrenal insufficiency 1, 3, 4
• Low or inappropriately normal ACTH with low cortisol indicates secondary adrenal insufficiency 1, 3, 4

Confirmatory Testing: Cosyntropin Stimulation Test

When morning cortisol levels are indeterminate (5-18 mcg/dL), the cosyntropin stimulation test must be performed to definitively rule out adrenal insufficiency. 1, 2, 3

Test Protocol:

• Administer 0.25 mg (250 mcg) cosyntropin intramuscularly or intravenously 1, 2, 3
• Measure serum cortisol at baseline, exactly 30 minutes, and 60 minutes post-administration 1, 2
• Peak cortisol >550 nmol/L (>18-20 mcg/dL) at either 30 or 60 minutes rules out adrenal insufficiency 1, 2, 3
• Peak cortisol <500 nmol/L (<18 mcg/dL) is diagnostic of adrenal insufficiency 1, 2, 3

Pediatric Dosing:

• Children <2 years: 0.125 mg (125 mcg) 2
• Children 2-17 years: 0.25 mg (250 mcg) 2

Supporting Laboratory Tests

Basic metabolic panel should be obtained to assess for electrolyte abnormalities commonly seen in adrenal insufficiency. 1

• Hyponatremia is present in 90% of newly diagnosed cases 1
• Hyperkalemia occurs in only ~50% of primary adrenal insufficiency cases, so its absence does not rule out the diagnosis 1, 4
• Hypoglycemia may occur, particularly in children 1

Etiologic Testing After Diagnosis

Once adrenal insufficiency is confirmed, determine the underlying cause:

• 21-hydroxylase autoantibodies should be measured first, as autoimmunity accounts for ~85% of primary adrenal insufficiency in Western populations 7, 1
• Adrenal CT imaging should be performed if autoantibodies are negative to evaluate for hemorrhage, tumors, tuberculosis, or other structural causes 7, 1
• Very long-chain fatty acids (VLCFA) should be measured in males to screen for adrenoleukodystrophy 7, 1

Critical Pitfalls to Avoid

Never delay treatment of suspected acute adrenal crisis to perform diagnostic testing—if the patient is clinically unstable with hypotension, altered mental status, or shock, immediately administer 100 mg IV hydrocortisone and 0.9% saline infusion at 1 L/hour. 1, 3

Exogenous steroids (prednisolone, dexamethasone, inhaled fluticasone) suppress the HPA axis and confound test results—glucocorticoids should be stopped on the day of testing, though long-acting steroids may require longer washout periods. 2, 1

If you must treat suspected adrenal crisis but still want to perform diagnostic testing later, use dexamethasone 4 mg IV instead of hydrocortisone, as dexamethasone does not interfere with cortisol assays. 1

The absence of hyperkalemia cannot rule out adrenal insufficiency, as it is present in only about 50% of cases. 1, 4

Estrogen-containing drugs should be stopped 4-6 weeks before cosyntropin testing, as they can affect cortisol-binding globulin levels and confound results. 2