This test measures two specific substances in your blood, metanephrine and normetanephrine, which are chemical byproducts formed when your body breaks down the stress hormones epinephrine (also called adrenaline) and norepinephrine.
These hormones are part of your body’s fight-or-flight response, which kicks in when you’re under physical or emotional stress. Once they’ve done their job, like raising your heart rate or blood pressure, they are broken down by an enzyme called catechol-O-methyltransferase (COMT) into metanephrine and normetanephrine, which then circulate in the blood.
This test is mainly used to help diagnose pheochromocytoma or paraganglioma, which are rare tumors that arise from adrenal gland tissue (or nearby nerve tissue) and cause an overproduction of epinephrine and norepinephrine. These tumors can lead to episodes of severely high blood pressure, headaches, sweating, and a racing heart.
Measuring free (unbound) metanephrines in plasma is currently one of the most sensitive methods for detecting these tumors. Sensitivity refers to a test’s ability to correctly identify people who do have a disease. However, the test is so sensitive that it can also pick up elevated levels from other causes, making specificity, its ability to rule out disease, somewhat lower.
Several factors can falsely raise your metanephrine levels even if you don’t have a tumor. These include stress, strenuous exercise, alcohol, caffeine, nicotine, and certain medications like decongestants, antidepressants, or blood pressure drugs. Conditions like heart failure or recent heart attacks can also interfere.
Because of this, you are typically asked to fast overnight, avoid stimulants like coffee or tobacco, and rest quietly before the blood is drawn.
