What urinary catecholamine and metanephrine levels are measured to diagnose a suspected pheochromocytoma?

Urinary Levels of Pheochromocytoma

For diagnosing pheochromocytoma, measure 24-hour urinary fractionated metanephrines (metanephrine and normetanephrine) and catecholamines (norepinephrine, epinephrine, and dopamine), with fractionated metanephrines being the most diagnostically reliable urinary test. 1, 2

Specific Urinary Tests to Order

Primary Urinary Tests

• 24-hour urinary fractionated metanephrines (metanephrine and normetanephrine): Sensitivity 77-97%, specificity 69-98% 1
• 24-hour urinary total metanephrines: Sensitivity approximately 95% 2, 3
• 24-hour urinary catecholamines (norepinephrine, epinephrine, dopamine): Traditional test but lower sensitivity 1

Additional Urinary Marker

• Urinary metanephrine to creatinine ratio: Sensitivity 100% 3

Test to Avoid

• Do NOT use vanillylmandelic acid (VMA) for screening - it has poor diagnostic reliability (only 38% in one study) and should not be used 1, 2, 3, 4

Diagnostic Thresholds

A 24-hour urine total metanephrine level above 1,800 mg (or μg) in the appropriate clinical setting is almost always diagnostic for pheochromocytoma. 1

For fractionated metanephrines, using a cut-off of twice the upper limit of normal provides optimal diagnostic performance with 95% sensitivity and 92.3% specificity 5. The sum of metanephrine and normetanephrine (urineMNM) ≥0.43 mg/24h yields 89% sensitivity and 96% specificity 6.

Important Collection Requirements

• Measure 24-hour urine creatinine concomitantly to confirm accurate collection 2
• Collect urine over a full 24-hour period for optimal sensitivity
• Multiple collections (2-3 consecutive days) may be needed for intermittent-secreting tumors 4

Comparison with Plasma Testing

While plasma free metanephrines have the highest overall sensitivity (97-100%) and specificity (85-89%) and are considered the best initial screening test 1, urinary measurements remain highly valuable because:

• Urinary tests have a lower false-positive rate compared to plasma tests 1
• They integrate catecholamine production over 24 hours, capturing episodic secretion
• They are more practical when proper plasma collection (supine position for 30 minutes) cannot be ensured 7
• Recent evidence shows plasma and urine metanephrines can be used interchangeably with good correlation 8

Common Pitfalls to Avoid

Medications That Cause False Positives

Discontinue these medications before testing to eliminate false-positive results 1:

• Tricyclic antidepressants
• Decongestants
• Amphetamines
• Reserpine
• Phenoxybenzamine
• Acetaminophen (interferes with certain measurement methods)

Clinical Situations Causing False Positives

• Acute illness or hospitalization 7
• Severe physiological stress
• Improper collection technique

When Results Are Borderline

If urinary metanephrine levels are only mildly elevated (less than 2-fold the upper limit):

1. Repeat the 24-hour urine collection to confirm results 3
2. Consider clonidine suppression test with plasma normetanephrine measurements 1, 2, 3, 9
3. Alternatively, measure plasma free metanephrines for additional confirmation 2, 3
4. In low-risk settings with borderline results, adopt a wait-and-retest approach after 6 months to detect progressive increases 7

Additional Biochemical Marker

For patients with suspected malignant pheochromocytoma or dopamine-secreting tumors, plasma methoxytyramine (MTY) provides useful information, though urine MTY is not helpful as it derives from renal DOPA metabolism rather than tumor production 10, 11.