Also Known As:
Metanephrines Normetanephrine Fractionated Metanephrines Free Metanephrines urine
Urine Metanephrines Total and Fractionated
What is Nor - Metanephrines - 24 hrs urine?
Metanephrine and normetanephrine are breakdown products (metabolites) of the catecholamines epinephrine (adrenaline) and norepinephrine. This test measures the amounts of metanephrine and normetanephrine that are released into the urine over a 24-hour period.
Catecholamines are produced by the adrenal glands (as hormones), small triangular organs located on top of each kidney, and by cells of the sympathetic nervous system (called neurotransmitter substances or neurotransmitters). The primary catecholamines are dopamine, epinephrine (adrenaline), and norepinephrine. Catecholamines are released 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 breakdown products are normally present in the urine in small fluctuating amounts that increase appreciably during and shortly after a stressful situation.
However, rare tumors of the adrenal gland called pheochromocytomas and rare tumors outside the adrenal glands called paragangliomas can produce large amounts of catecholamines and their metabolites, resulting in greatly increased concentrations in both the blood and urine. (These syndromes are often grouped together and abbreviated as PPGL). 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, hypertension caused by the excess hormones may cause kidney damage, and heart disease, and raise the risk of a stroke or heart attack.
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 number 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. Empty the bladder completely without collecting. Then collect urine for 24 hours only – no more than 24 hours. It is important that the sample be refrigerated during this time.
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 the correct interpretation of results. Follow any instructions given by your health care practitioner or the collection site or laboratory.
- You should talk to your health care provider about prescription medications and over-the-counter drugs and supplements that you are taking. It may be necessary to discontinue medications for some time prior to the test.
- However, you should not stop taking any medications without consulting your healthcare provider. Your health practitioner will work with you to identify potentially interfering substances and drug treatments and to determine which of them can be safely interrupted and which must be continued for your well-being.
- You will also be instructed on what foods to avoid.
- Avoid emotional and physical stresses and vigorous exercise prior to and during sample collection as they can increase catecholamine release and therefore affect metanephrine levels.