Metanephrine, Plasma Unit Converter

Plasma metanephrine is a metabolite of epinephrine (adrenaline). It is produced when the enzyme catechol-O-methyltransferase (COMT) breaks down epinephrine inside adrenal chromaffin cells.

This test measures the free (unconjugated) form of metanephrine circulating in the blood. It is most commonly ordered alongside normetanephrine (the corresponding metabolite of norepinephrine) as part of a fractionated plasma metanephrines panel.

Because metanephrine is produced continuously within chromaffin cells, independent of episodic catecholamine release, it serves as a reliable marker for catecholamine-secreting tumors such as pheochromocytoma and paraganglioma.

Metanephrine is produced primarily within the chromaffin cells of the adrenal medulla, where the enzyme COMT converts epinephrine leaking from storage granules into the cytoplasm. Small amounts may also be generated at sites of extraneuronal catecholamine metabolism.