What is the appropriate evaluation for suspected pheochromocytoma?

Evaluation for Pheochromocytoma

Initial biochemical testing should measure plasma free metanephrines or urinary fractionated metanephrines, with plasma free metanephrines being the single most accurate test when performed correctly 1, 2.

Biochemical Testing Algorithm

First-Line Testing

• Plasma free metanephrines (preferred when done correctly):

  • Sensitivity: 99% 2
  • Specificity: 89% 2
  • Critical collection requirements: Patient must be supine for 30 minutes before blood draw, fasting overnight if methoxytyramine is measured 3
  • Use age-adjusted reference intervals 3
  • If these conditions cannot be met, use urinary testing instead

• Urinary fractionated metanephrines (more practical for most settings):

  • Sensitivity: 97% 2
  • Specificity: 69% 2
  • Better for mainstream use when proper plasma collection cannot be ensured 3
  • 24-hour urine collection

Laboratory Method

Use liquid chromatography with mass spectrometry (LC-MS/MS) or electrochemical detection rather than other methods 1, 3. This is particularly important when measuring methoxytyramine (the O-methylated metabolite of dopamine), which helps identify extra-adrenal paragangliomas and metastatic disease 3.

Imaging After Positive Biochemical Testing

Initial Localization

• CT scan is the suggested first-line imaging modality 1
• MRI is preferred in:
  • Patients with metastatic disease 1
  • When radiation exposure must be limited (pregnancy, children, young patients with hereditary syndromes) 1

Functional Imaging

• 123I-MIBG scintigraphy is useful for metastatic disease 1
• Newer options like 99mTc-labeled somatostatin receptor imaging show 94.4% sensitivity for detecting pheochromocytomas and identifying metastases 4, though this represents a cost-effective alternative rather than first-line choice

Genetic Testing

Consider genetic testing in ALL patients with confirmed pheochromocytoma 1. This is particularly important because:

• Patients with paragangliomas should be tested for SDHx mutations 1
• Those with metastatic disease should be tested for SDHB mutations 1
• Younger patients, those with tumors ≥5 cm, norepinephrine-secreting tumors, and bilateral disease have higher likelihood of germline mutations 5
• Use accredited laboratories only 1

Critical Preanalytical Factors to Avoid False Results

False-Positive Causes

• Improper blood collection (not supine, not fasting) 1, 3
• Medications (tricyclic antidepressants, sympathomimetics, certain antihypertensives)
• Stress during collection
• Renal insufficiency

False-Negative Causes

• Small tumors (<1 cm)
• Cystic or necrotic tumors with minimal functional tissue
• Intermittent catecholamine secretion

Follow-Up of Positive Results

All positive biochemical results require appropriate follow-up 1. The extent and pattern of metanephrine elevation can predict:

• Tumor size (higher levels = larger tumors) 3
• Location (adrenal vs. extra-adrenal) 3
• Presence of metastases 3
• Underlying genetic mutations 3

A noradrenergic secretion profile (elevated normetanephrine) is associated with symptomatic presentation (OR 12.73) and increased perioperative complications 6.

Common Pitfalls

• Do not rely on plasma catecholamines alone (only 84% sensitivity) 2
• Avoid urinary VMA as primary test (only 64% sensitivity) 2
• Do not skip genetic testing even in apparently sporadic cases—hereditary syndromes are more common than previously recognized 5
• Ensure proper plasma collection technique or default to urine testing 3