The Test Sample
What is being tested?
Vanillylmandelic acid (VMA) is one of the metabolites of the catecholamines epinephrine (adrenaline) and norepinephrine. This test measures the amount of VMA that is excreted into the urine, typically over a 24-hour period, to detect excess catecholamine production.
Catecholamines are a group of similar hormones produced in the central portion of the adrenal glands, the adrenal medulla. Adrenal glands are small triangular organs located on top of each kidney. The primary catecholamines that they release are dopamine, epinephrine, and norepinephrine. These hormones are released into the bloodstream in response to physical or emotional stress. They help transmit nerve impulses in the brain, increase glucose and fatty acid release for energy, dilate bronchioles, and dilate the pupils. Norepinephrine also constricts blood vessels, increasing blood pressure, and epinephrine increases heart rate and metabolism. After completing their actions, the catecholamines are metabolized to inactive compounds. Dopamine becomes homovanillic acid (HVA), norepinephrine breaks down into normetanephrine and VMA, and epinephrine becomes metanephrine and VMA. Both the hormones and their metabolites are excreted in the urine.
VMA is usually present in the urine in small fluctuating amounts that only increase appreciably during and shortly after the body is exposed to a stressor. Neuroblastomas, pheochromocytomas, and other neuroendocrine tumors, however, can produce large amounts of catecholamines, resulting in greatly increased concentrations of the hormones and their metabolites. The hormone releases can cause persistent hypertension, severe headaches, palpitations, sweating, nausea, anxiety, and tingling in the extremities.
Neuroblastomas are rare cancers but, according to the American Cancer Society, they are the most common cancers affecting infants. About 700 new cases are diagnosed each year, primarily in babies one to two years old, with up to 90% of cases occurring in children under the age of five. Rarely, a baby may be born with a neuroblastoma. Arising from primitive nerve cells, the cancers can be found in the abdomen, adrenal glands, neck, chest, or pelvis. About two-thirds of the time, the tumors will have metastasized and moved to other parts of the body by the time they are diagnosed. Once detected, many neuroblastomas can be successfully treated. In some cases, neuroblastomas may disappear on their own or their cells may spontaneously mature into normal nerves cells, turning the neuroblastoma into a benign ganglioneuroma or into a partially benign ganglioneuroblastoma.
Pheochromocytomas are rare tumors that arise primarily in the adrenal glands. According to the National Cancer Institute, they affect 2 to 8 people per million per year, primarily those in their thirties to fifties. Most pheochromocytomas are benign and do not spread from their original location, but some may metastasize and move to other organs within the body. Left untreated, they continue to grow and produce catecholamines, and hormone-related symptoms continue to worsen. Over time, the hypertension that the pheochromocytoma causes may damage body organs, such as the kidneys and heart, and raise the risk of an affected person having a stroke or heart attack. Pheochromocytomas are important to diagnose because they represent a potentially curable form of hypertension. In most cases, they can be removed and/or treated to reduce or eliminate the associated symptoms and complications.
The VMA test, along with other tests for catecholamines and their metabolites, can be used to help detect the presence of neuroblastomas and pheochromocytomas.
How is the sample collected for testing?
For a 24-hour urine collection, all of the urine produced during a 24-hour period should be saved. It is important that the sample be refrigerated during this time period. A single urine sample is collected for a random urine test.
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?
This test is affected by caffeine, certain drugs, and stresses. It is important to inform the health care provider of any medications being taken, including herbal supplements and over-the-counter products, and to follow any instructions provided for things to avoid before sample collection.