Best Test for Pheochromocytoma
Plasma free metanephrines is the single best initial test for diagnosing pheochromocytoma, offering the highest sensitivity (99%) and excellent specificity (89%). 1
Primary Recommendation
Measure plasma free metanephrines (metanephrine and normetanephrine) as your first-line diagnostic test. This test achieves 97-99% sensitivity with 89% specificity, outperforming all other biochemical tests 1, 2. The 2007 European Society of Hypertension/Cardiology guidelines explicitly state this is the test of choice when available for routine diagnosis 1.
Alternative When Plasma Testing Unavailable
If plasma free metanephrines are not available at your institution, use 24-hour urinary fractionated metanephrines as the alternative first-line test 3, 1. This achieves 97% sensitivity but lower specificity (69%) compared to plasma testing 2.
Algorithmic Approach to Testing
Step 1: Initial Biochemical Testing
- Order plasma free metanephrines (metanephrine + normetanephrine)
- If values are >4 times the upper reference limit, the diagnosis is essentially confirmed—proceed directly to imaging 1
- Reference intervals should favor sensitivity over specificity to avoid missing cases 4
Step 2: Managing Equivocal Results
When plasma or urine values show only modest elevation (less than 4-fold):
- Perform clonidine suppression test: A marked reduction in plasma catecholamines indicates a negative result 1, 5
- Consider 24-hour urine collection for catecholamines and metanephrines if plasma testing was equivocal 6
Step 3: Supplementary Testing (Optional)
Adding 3-methoxytyramine to plasma metanephrines can increase sensitivity from 93.9% to 97% 7. This is particularly valuable for detecting:
- Dopamine-producing tumors
- Biochemically silent pheochromocytomas
- Assessing malignancy likelihood 3
Do NOT routinely add chromogranin A—it significantly reduces specificity from 91.3% to 75% without improving diagnostic accuracy 7.
Tests to Avoid as Initial Screening
The following tests have inferior diagnostic performance and should not be used for initial diagnosis:
- Plasma catecholamines alone: only 84% sensitivity 2
- Urinary catecholamines: only 86% sensitivity 2
- Urinary total metanephrines: only 77% sensitivity 2
- Urinary vanillylmandelic acid (VMA): only 64% sensitivity 2
Critical Clinical Context
When to Test
Test for pheochromocytoma in patients with:
- Hypertension (sustained or paroxysmal) PLUS the classic triad: headache, palpitations, sweating 1
- Hypertensive patients over age 30 who are pregnant 6
- Incidentally discovered adrenal mass with any hypertensive features 3
- Known genetic syndromes (NF1, MEN2, VHL, SDHx mutations) 6, 8
Important Caveats
- Never perform fine needle biopsy of a suspected pheochromocytoma—this is absolutely contraindicated due to risk of catecholamine crisis 3
- Biochemical testing must always precede imaging to avoid unnecessary radiation exposure and guide appropriate imaging modality 4
- For imaging localization after biochemical confirmation, prefer MRI over CT to avoid hypertensive crisis from IV contrast 3
Evidence Quality
The recommendation for plasma free metanephrines comes from a large multicenter cohort study of 858 patients (214 with confirmed pheochromocytoma, 644 without) that directly compared all available biochemical tests 2. This study demonstrated that combining different tests does not improve diagnostic yield beyond plasma free metanephrines alone. The European guidelines 1 adopted these findings, though acknowledging the formal evidence level is low despite high diagnostic accuracy.