Pheochromocytoma laboratory findings

Laboratory findings consistent with the diagnosis of pheochromocytoma include elevated 24-hour urinary fractionated catecholamines and metanephrines for low-risk patients and plasma fractionated metanephrines for high-risk patients.

An elevated concentration of the following is diagnostic of pheochromocytoma.

• Elevated 24-hour urine fractionated metanephrines and catecholamines. The cutoff values are: ^[1]
  • Normetanephrine >900 mcg/24 hours
  • Metanephrine >400 mcg/24 hours
  • Norepinephrine >170 mcg/24 hours
  • Epinephrine >35 mcg/24 hours
  • Dopamine >700 mcg/24 hours
• Elevated plasma fractionated metanephrines. The cutoff values are:
  • Metanephrine > 0.3-0.5 nmol/L
  • Normetanephrine > 0.66- 0.9 nmol/L ^{[2] [3]}

• Elevated urinary vanillyl mandelic acid ^{[4] [2]}

The following drugs interfere with urinary catecholamines metabolism and shoudl be discontinued two weeks before any hormonal assessments: ^[5]

• Tricyclic antidepressants (TCAs)
• Levodopa
• Antipsychotics
• Ethanol
• Acetaminophen
• Phenoxybenzamine ^[6]

Patients with spells of elevated blood pressure (sudden onset of a symptom or symptoms) can be negative in-between spells and should be tested directly after the attacks.^[7]