What Metanephrine Tests Screen For
Metanephrine and normetanephrine tests (plasma or urine) screen for pheochromocytoma and paraganglioma—rare catecholamine-secreting tumors that cause dangerous hypertension and can be fatal if undiagnosed. 1
Understanding the Test
- Metanephrines are breakdown products (metabolites) of adrenaline and noradrenaline, the hormones that control your "fight or flight" response 2
- Your body normally produces small amounts of these metabolites, but pheochromocytomas produce massive amounts continuously, even when the tumor isn't actively releasing hormones into your bloodstream 3, 2
- This makes metanephrine testing more reliable than measuring the hormones themselves, which can be normal between episodes 3
Why This Test Matters
- Pheochromocytomas cause severe, sometimes life-threatening complications including heart attacks, strokes, sudden cardiac arrest, and hypertensive crises that can be fatal 1
- These tumors are present in 0.01-0.2% of people with high blood pressure, but up to 4% of those with resistant hypertension (blood pressure that won't respond to multiple medications) 1
- About 35% of cases are hereditary, so finding one case can lead to screening family members and potentially saving lives 1
When Doctors Order This Test
Your doctor will order metanephrine testing if you have: 1
- The classic triad: severe headaches, palpitations (racing heart), and excessive sweating occurring together—this combination has 90% accuracy for the diagnosis
- Resistant hypertension that doesn't respond to three or more blood pressure medications
- Paroxysmal (episodic) hypertension with sudden spikes in blood pressure
- Family history of pheochromocytoma or related genetic syndromes
- Young age at hypertension onset (under 30 years old)
Test Accuracy
- Plasma free metanephrines have 96-100% sensitivity, meaning they catch virtually all cases 1, 4
- Normal results essentially rule out pheochromocytoma with 100% certainty 3
- Urine metanephrines are slightly less sensitive (86-97%) but still highly accurate 1, 5
Important Testing Details
- For plasma testing, you should lie down for 30 minutes before the blood draw to avoid false elevations—sitting can raise results by 25% 6
- Results more than 4 times the normal limit are diagnostic and require immediate imaging to locate the tumor 1, 4
- Mildly elevated results (1-2 times normal) may need repeat testing under ideal conditions or additional specialized tests 1
What Happens After a Positive Test
- Imaging (preferably MRI) locates the tumor without triggering a dangerous blood pressure crisis 1, 4
- Genetic testing is recommended for all patients since one-third have hereditary forms 1, 4
- Specialized blood pressure medications (alpha-blockers) must be started before any surgery to prevent life-threatening complications 1, 4
Critical Safety Point
Never have a biopsy of a suspected pheochromocytoma—this can trigger a fatal hypertensive crisis. 1 The diagnosis is made biochemically with metanephrine testing and confirmed with imaging, not tissue sampling.