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The Test Sample
What is being tested?
Metanephrine and normetanephrine are breakdown products (metabolites) of epinephrine (adrenaline) and norepinephrine. Epinephrine and norepinephrine belong to a group of similar hormones called catecholamines. This test measures the amounts of metanephrine and normetanephrine that are released into the urine over a 24-hour period.
Catecholamines are produced in the adrenal medulla, the central portion of the adrenal glands, small triangular organs located on top of each kidney and by cells of the sympathetic nervous system. The primary catecholamines are dopamine, epinephrine (adrenaline), and norepinephrine. These hormones are released into the blood in response to physical or emotional stress. They help transmit nerve impulses in the brain, increase glucose and fatty acid release for energy, dilate small air passages in the lungs called bronchioles, and dilate the pupils. Norepinephrine also constricts blood vessels, which increases blood pressure, and epinephrine increases heart rate and the rate at which the body uses energy (metabolism).
After completing their actions, the catecholamines are broken down to form inactive compounds. Epinephrine breaks down into metanephrine and vanillylmandelic acid (VMA), and norepinephrine becomes normetanephrine and VMA. Both the hormones and their metabolites are eliminated from the body in the urine.
Catecholamines and their metabolites are normally present in the urine in small fluctuating amounts that increase appreciably during and shortly after a stressful situation.
However, rare adrenal tumors called pheochromocytomas and rare extra-adrenal tumors called paragangliomas can produce large amounts of the hormones and their metabolites, resulting in greatly increased concentrations in both the blood and urine. This can cause persistent or episodic periods of hypertension, which may lead to severe headaches. Other symptoms include heart palpitations, sweating, nausea, anxiety, and tingling in the hands and feet.
Pheochromocytomas and paragangliomas are rare. While a few are cancerous, most are benign and do not spread beyond their original location. Left untreated, however, these tumors may continue to grow and the symptoms may worsen. Over time, the hypertension caused by the excess hormones may cause kidney damage, heart disease, and raise the risk of a stroke or heart attack.
The Endocrine Society recommends that a test for plasma free metanephrine or urine metanephrine be used as the primary test to help detect the presence of pheochromocytomas and paragangliomas. Although they are rare, it is important to diagnose and treat these tumors because they cause a potentially curable form of hypertension. In most cases, the tumors can be surgically removed and/or treated to eliminate or significantly reduce the amount of catecholamines being produced and to reduce or eliminate associated symptoms and complications.
How is the sample collected for testing?
For the 24-hour urine collection, all urine should be saved for a 24-hour period. It is important that the sample be refrigerated during this time period.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Catecholamine levels, and by extension the levels of their metabolites, are affected by various drugs, foods and stresses. Preparation for the test is important to ensure that an appropriate sample is collected and for correct interpretation of results. Follow any instructions given by the healthcare provider or the collection site or laboratory.
- People being tested should talk to their healthcare provider about prescription medications and over-the-counter drugs and supplements that they are taking. It may be necessary to discontinue medications for some time prior to the test. However, the patient should not stop taking any medications without consulting their healthcare provider.
- The patient will also be instructed on what foods to avoid.
- Emotional and physical stresses and vigorous exercise should be minimized prior to and during sample collection as they can increase catecholamine secretion and therefore affect metanephrine levels.