What laboratory tests are recommended for the workup of adrenal nodules?

Laboratory Workup for Adrenal Nodules

All patients with adrenal incidentalomas require screening for autonomous cortisol secretion with a 1 mg overnight dexamethasone suppression test, and selective screening for primary aldosteronism and pheochromocytoma based on specific clinical and radiological criteria. 1

Mandatory Testing for All Adrenal Nodules

Cortisol Screening (Universal)

• Perform a 1 mg overnight dexamethasone suppression test in every patient with an adrenal incidentaloma - this is the preferred initial screening method regardless of symptoms or imaging characteristics 1, 2
• Administer 1 mg dexamethasone at 11 PM and measure serum cortisol at 8 AM the following morning 1, 2, 3
• Interpret results as follows: 1, 2
  • ≤50 nmol/L (1.8 μg/dL): excludes cortisol hypersecretion
  • 51-138 nmol/L (1.9-5.0 μg/dL): possible autonomous cortisol secretion

  • 138 nmol/L (>5.0 μg/dL): evidence of cortisol hypersecretion

• Measure plasma ACTH levels to confirm ACTH independency in all patients with abnormal dexamethasone suppression who are being considered for intervention 1, 3
• Consider 24-hour urinary free cortisol and midnight salivary cortisol as ancillary tests when results are equivocal 1, 3

Selective Testing Based on Clinical Presentation

Primary Aldosteronism Screening (Hypertension/Hypokalemia)

• Measure aldosterone-to-renin ratio (ARR) in all patients with hypertension and/or hypokalemia 1, 2
• Obtain the sample in the morning after the patient has been out of bed for 2 hours and seated for 5-15 minutes 1
• An ARR >20 ng/dL per ng/mL/hr has excellent sensitivity and specificity (>90%) for confirming hyperaldosteronism 1, 2, 4
• Critical pitfall: Ensure patients are potassium-replete and substitute interfering medications before testing when possible 1, 2
• Confirmatory testing includes saline suppression and salt loading with 24-hour urine aldosterone measurement 1
• Adrenal vein sampling is required for lateralization prior to offering adrenalectomy 1

Pheochromocytoma Screening (Selective Indications)

• Do NOT screen patients with unequivocal adrenocortical adenomas (HU <10 on non-contrast CT) who have no signs or symptoms of adrenergic excess 1
• Screen for pheochromocytoma if either condition is present: 1, 2
  • Adrenal mass displays ≥10 HU on non-contrast CT
  • Signs/symptoms of catecholamine excess (headaches, anxiety attacks, sweating, palpitations, episodic hypertension)
• Measure plasma free metanephrines or 24-hour urinary fractionated metanephrines and normetanephrines 1, 2
• Levels >2X upper limit of normal are diagnostic 1
• Critical pitfall: Never perform adrenal biopsy without first excluding pheochromocytoma, as biopsy of undiagnosed pheochromocytoma triggers life-threatening hypertensive crisis 3

Androgen Screening (Virilization/Suspected Malignancy)

• Perform serum androgen testing when: 1, 2
  • Clinical signs of virilization are present (hirsutism, acne, menstrual irregularities in females)
  • Adrenocortical carcinoma is suspected
  • Bilateral adrenal masses are present (consider congenital adrenal hyperplasia)
• Measure DHEA-S and testosterone as initial tests 1, 2, 3
• Extended panel includes 17β-estradiol, 17-OH progesterone, androstenedione, 17-OH pregnenolone, 11-deoxycorticosterone, progesterone, and estradiol when initial tests are abnormal 1, 3
• Higher androgen levels suggest greater burden of disease and increased likelihood of adrenocortical carcinoma 1

Algorithm for Laboratory Testing

Step 1: Perform 1 mg overnight dexamethasone suppression test on ALL patients 1, 2

Step 2: Assess for hypertension and/or hypokalemia

• If present → measure aldosterone-to-renin ratio 1, 2
• If absent → proceed to Step 3

Step 3: Review non-contrast CT attenuation values

• If HU ≥10 OR patient has symptoms of catecholamine excess → measure plasma free metanephrines or 24-hour urinary metanephrines 1, 2
• If HU <10 AND no symptoms → pheochromocytoma screening not required 1

Step 4: Assess for virilization or suspected adrenocortical carcinoma

• If present → measure DHEA-S and testosterone 1, 2
• If absent → no androgen testing needed

Important Clinical Considerations

Medication Interference

• Multiple medications interfere with hormone testing results, particularly aldosterone-to-renin ratio testing 2, 3
• Hold interfering medications before testing when clinically safe to do so 2, 3

Follow-up Hormonal Testing

• No repeat functional testing is required for benign non-functional adenomas <4 cm, myelolipomas, and other small masses containing macroscopic fat 2
• For indeterminate masses that grow >5 mm/year, repeat the complete functional workup before considering surgical intervention 2
• For masses growing 3-5 mm/year, continued surveillance may be appropriate without extensive hormonal retesting 2

Prevalence Context

• Approximately 5.3% of adrenal incidentalomas are cortisol-secreting adenomas 2, 3
• 1% are aldosterone-secreting adenomas 2, 3
• 5.1% are pheochromocytomas 2, 3
• The risk of malignant transformation in benign-appearing lesions with minimal growth is extremely low (0-1%) 2

Common Pitfalls to Avoid

• Failing to screen for autonomous cortisol secretion in asymptomatic patients - this is mandatory for all adrenal incidentalomas 1, 2
• Screening for pheochromocytoma in patients with lipid-rich adenomas (HU <10) without symptoms - this wastes resources and may cause unnecessary anxiety 1
• Assuming radiological appearance predicts hormone secretion status - imaging characteristics cannot reliably exclude functional tumors 3
• Performing adrenal biopsy before excluding pheochromocytoma - this can be fatal 3