What laboratory tests should be ordered to evaluate adrenal function, including assessment for adrenal insufficiency and excess?

Bloodwork to Test for Adrenal Function

For evaluating adrenal function, start with morning (8 AM) serum cortisol and plasma ACTH levels, along with a basic metabolic panel to assess electrolytes—this initial workup will guide whether you need dynamic testing or can rule out adrenal dysfunction immediately. 1

Initial Screening Tests

For Suspected Adrenal Insufficiency

• Measure morning (8 AM) serum cortisol and plasma ACTH simultaneously as your first-line tests when adrenal insufficiency is suspected 1, 2
• Obtain a basic metabolic panel (sodium, potassium, CO2, glucose) to look for hyponatremia, hyperkalemia, acidosis, or hypoglycemia—classic electrolyte abnormalities in adrenal insufficiency 1

Interpretation of morning cortisol in acute illness:

• Cortisol <250 nmol/L (9 μg/dL) with elevated ACTH is diagnostic of primary adrenal insufficiency 1
• Cortisol <400 nmol/L (14.5 μg/dL) with elevated ACTH raises strong suspicion of primary adrenal insufficiency 1
• If morning cortisol is ≥354 nmol/L, adrenal insufficiency is effectively ruled out and dynamic testing can be avoided 3

Critical pitfall: Never delay treatment in suspected acute adrenal crisis while waiting for test results—give hydrocortisone 100 mg IV/IM immediately and diagnose later 1

For Suspected Adrenal Excess (Cushing's Syndrome)

The 1 mg overnight dexamethasone suppression test (DST) is the preferred initial screening test for autonomous cortisol secretion 4, 2:

• Give 1 mg dexamethasone at 11 PM
• Measure serum cortisol at 8 AM the next morning
• Cortisol ≤50 nmol/L excludes cortisol hypersecretion 4
• Cortisol 51-138 nmol/L suggests possible autonomous cortisol secretion 4
• Cortisol >138 nmol/L indicates evidence of cortisol hypersecretion 4

Alternative screening tests (when DST is not suitable):

• Late night salivary cortisol (LNSC) is the most specific screening test and particularly useful for cyclic Cushing's syndrome 2
• 24-hour urinary free cortisol (UFC) measures total daily cortisol production but has the lowest sensitivity among screening tests 2

Important caveat: False positive DST results occur with rapid dexamethasone metabolism (CYP3A4 inducers), malabsorption, or increased cortisol-binding globulin 2

Dynamic Testing When Needed

Short Synacthen Test (ACTH Stimulation Test)

When to perform:

• Morning cortisol is indeterminate (between 126-354 nmol/L in follow-up cases, or <400 nmol/L in acute illness) 1, 5, 3
• Clinical suspicion remains high despite borderline morning cortisol 4

Dosing per FDA label:

• Adults: 250 μg (0.25 mg) cosyntropin IV or IM 6
• Children <2 years: 125 μg (0.125 mg) 6
• Children 2-17 years: 250 μg (0.25 mg) 6

Interpretation:

• Measure cortisol at baseline, 30 minutes, and 60 minutes post-injection 6
• Peak cortisol <500 nmol/L (18 μg/dL) at 30 or 60 minutes is diagnostic of adrenal insufficiency 2, 6
• Peak cortisol ≥420 nmol/L rules out adrenal insufficiency 3

Key pitfall: Stop glucocorticoids and spironolactone on the day of testing; long-acting glucocorticoids may need longer washout 6

Hormone-Specific Testing for Adrenal Excess

Primary Aldosteronism (Hyperaldosteronism)

When to test: Patients with hypertension and/or hypokalemia 4

• Measure aldosterone/renin ratio (ARR) as the preferred initial test 4
• Perform in the morning after patient has been upright for 2 hours and seated for 5-15 minutes 4
• Ensure patient is potassium-replete and off interfering medications 4
• ARR >20 ng/dL per ng/mL/hr has >90% sensitivity and specificity for confirming hyperaldosteronism 4

Confirmatory testing: Saline suppression test or salt loading with 24-hour urine aldosterone measurement 4

Pheochromocytoma

When to test: Adrenal masses ≥10 HU on non-contrast CT or signs/symptoms of catecholamine excess 4

• Measure plasma free metanephrines as the screening test 4
• Alternatively, 24-hour urinary metanephrines can be used 4
• Levels >2X upper limit of normal are diagnostic 4

Androgen Excess

When to test: Suspected adrenocortical carcinoma (ACC) or clinical virilization 4

• Measure DHEAS and testosterone as initial tests 4
• Higher levels suggest greater disease burden 4
• Extended panel if needed: 17β-estradiol, 17-OH progesterone, androstenedione, 17-OH pregnenolone, 11-deoxycorticosterone, progesterone, and estradiol 4

Determining Etiology of Adrenal Insufficiency

Once adrenal insufficiency is confirmed:

• Measure 21-hydroxylase (anti-adrenal) autoantibodies to identify autoimmune etiology 1
• If antibodies are negative, obtain adrenal CT imaging to evaluate for hemorrhage, tumor, or infection 1
• In male patients, measure very long-chain fatty acids to screen for adrenoleukodystrophy 1
• Plasma ACTH level distinguishes primary from secondary adrenal insufficiency: elevated ACTH indicates primary (adrenal) disease, while low/normal ACTH suggests secondary (pituitary/hypothalamic) disease 1, 2

Medication Considerations

Stop these medications before testing:

• Glucocorticoids and spironolactone: Stop on the day of ACTH stimulation testing 6
• Estrogen-containing drugs: Stop 4-6 weeks before testing, as they increase cortisol-binding globulin and falsely elevate total cortisol levels 6
• CYP3A4 inducers: May cause false positive DST results 2

Follow-Up Testing

• For confirmed primary adrenal insufficiency: Monitor TSH, free T4, TPO antibodies, glucose, HbA1c, complete blood count, and vitamin B12 annually to screen for associated autoimmune conditions 4
• For adrenal axis recovery monitoring: A morning cortisol ≤126 nmol/L indicates ≥95% chance of persistent insufficiency, eliminating the need for repeat ACTH stimulation testing 5