Urine Metanephrines

Function and Clinical Purpose

Urine metanephrines are the metabolites of catecholamines (epinephrine and norepinephrine). The adrenal glands normally produce these hormones in response to stress. However, certain rare tumors secrete these hormones continuously or in large bursts. Measuring metanephrines in a 24-hour urine collection is often more sensitive than measuring the hormones themselves, as the metabolites remain stable in the urine over a longer period.

Why it is Ordered

This test is the primary screening tool for catecholamine-secreting tumors. It is ordered for patients presenting with the classic triad of symptoms: episodic headaches, sweating (diaphoresis), and a racing heart (tachycardia), especially when accompanied by difficult-to-control high blood pressure. Key indications include:

• Pheochromocytoma: A tumor of the adrenal gland.
• Paraganglioma: A tumor of the extra-adrenal sympathetic or parasympathetic nervous system.
• Incidentaloma: When an imaging study (CT or MRI) unexpectedly reveals an adrenal mass.

Associated Conditions

Elevated metanephrines are most commonly associated with pheochromocytoma, which, while rare, is a critical diagnosis because it is a surgically curable cause of hypertension. If missed, it can lead to severe cardiovascular events, including stroke or heart attack. Because some of these tumors are associated with genetic syndromes like Multiple Endocrine Neoplasia Type 2 (MEN2), Von Hippel-Lindau (VHL) disease, or Neurofibromatosis Type 1, a positive result may trigger genetic counseling and screening for other family members.