Screening Tests for Pheochromocytoma Without 24-Hour Urine Collection
Plasma free metanephrines is the optimal screening test for pheochromocytoma, offering the highest sensitivity (96-100%) and good specificity (89-98%) without requiring 24-hour urine collection. 1
Diagnostic Options for Pheochromocytoma
First-Line Test: Plasma Free Metanephrines
- Highest sensitivity (96-100%) and good specificity (89-98%) 1, 2
- Should be collected after patient has been lying supine for 30 minutes 1
- Requires only a single blood draw
- Results >4 times upper limit of normal are consistent with pheochromocytoma 1
- For borderline elevations, consider clonidine suppression test 1
Alternative Options
- Single-voided ("spot") urine metanephrine and normetanephrine assay
- Sensitivity 97.6% and specificity 100% when using cutoff value of >500 ng/mg creatinine for either metanephrine or normetanephrine 3
- Convenient for outpatients
- Does not require 24-hour collection
Testing Protocol
Preparation for Testing
- Avoid interfering foods and medications prior to testing:
- Caffeine, alcohol, acetaminophen
- Tricyclic antidepressants, MAO inhibitors
- Sympathomimetics (decongestants)
- Patient should be in a relaxed state
Interpretation of Results
- Plasma free metanephrines:
Special Considerations
High-Risk Populations
- Consider genetic testing for patients with:
- Young age at diagnosis
- Family history of pheochromocytoma
- Bilateral or multifocal disease
- Extra-adrenal location 1
Common Pitfalls
- False positives can occur with:
- Acute stress
- Medications (as listed above)
- Improper sample collection (not collected in supine position)
- False negatives are rare with plasma free metanephrines (missed cases <1%) 2
Comparative Test Performance
| Test | Sensitivity | Specificity | Comments |
|---|---|---|---|
| Plasma free metanephrines | 96-100% | 89-98% | Best first-line test [1,2] |
| Urinary fractionated metanephrines (24h) | 97% | 69% | Good sensitivity but requires 24h collection [2] |
| Plasma catecholamines | 76-84% | 81-88% | Lower sensitivity [5,2] |
| Single-voided urine metanephrines | 97.6% | 100% | Good alternative to 24h collection [3] |
The European Society of Hypertension and European Society of Cardiology guidelines confirm that measurement of plasma free metanephrines provides the highest sensitivity for diagnosis of pheochromocytoma 4, making it the preferred screening test when 24-hour urine collection is not feasible or practical.