The vanillylmandelic acid (VMA) test is primarily used to detect and rule out neuroblastomas in children with an abdominal mass or other symptoms suggestive of the disease. It may be ordered along with an homovanillic acid (HVA) test to help diagnose a neuroblastoma, to monitor the effectiveness of treatment, and to monitor for neuroblastoma recurrence. A urine creatinine is typically also ordered, especially with random urine testing, and tests results are frequently reported as VMA-to-creatinine and HVA-to-creatinine ratios. Since creatinine is a substance that is excreted in the urine at a relatively constant rate, it serves as a comparison to the rate of VMA and HVA excretion.
VMA testing is ordered when a doctor either suspects that a child has a neuroblastoma or wants to rule out the possibility. The doctor may order it, along with an homovanillic acid (HVA) test, when a child has an abdominal mass or other symptoms suggestive of a neuroblastoma. These signs and symptoms can vary depending upon their location and may vary over time:
Most neuroblastomas are located in the belly, so the most common symptom is an unusual non-tender lump or mass in that area. Others include abdominal pain and lack of appetite.
Sometimes a tumor in the neck can cause swelling and affect swallowing or breathing.
If the tumor presses on nerves by the spine, it may affect the child's ability to walk.
If it has spread to the bones (metastasized), it may cause bone pain, and if to the marrow, it may affect blood cell production, causing fatigue, pallor, and bleeding.
A neuroblastoma can also cause bruising around the eyes and drooping eyelids, bluish purple spots on the skin, and can sometimes affect bladder and bowel function. Rarely, it may cause muscle spasms and rapid eye movements referred to as "dancing eyes, dancing feet."
The VMA test may also be ordered when a child has been treated for a neuroblastoma and ordered periodically to monitor for recurrence.
A VMA test may be ordered along with one or more metanephrine or catecholamine tests when a doctor suspects that a person has a pheochromocytoma. They may be ordered when a person has persistent or recurring hypertension that is not responding to conventional therapies, to monitor the effectiveness of treatment for a pheochromocytoma, and periodically to monitor for recurrence.
Since the VMA test is sensitive to many outside influences, and neuroblastomas and pheochromocytomas are rare, a doctor may see more false positives with this test than true positives. When a person has large amounts of VMA in his urine, it is not diagnostic of a condition; it is an indication that further investigation is necessary.
Intense emotional and physical stresses can cause moderate to large temporary increases in VMA levels. The doctor must evaluate the child or adult as a whole – his physical condition, emotional state, prescribed medications, and any over-the-counter products that he is taking. When interfering substances and/or conditions are found and resolved, the doctor will frequently re-test the person to determine whether the VMA is still elevated. The doctor may also order other catecholamine and metanephrine testing and imaging tests, such as an MRI, to help find the tumor(s).
If a child or adult is being treated for a neuroblastoma or pheochromocytoma, then decreasing VMA concentrations indicate a response to treatment; stable or increasing levels indicate that the treatment is not effective. If a VMA concentration is initially normal and then increases in a person who has had a previous neuroblastoma or pheochromocytoma, then it is likely that the tumor is recurring.
About 90% of children with a neuroblastoma will produce excess VMA and homovanillic acid. If a VMA and other catecholamine and metanephrine testing are normal, then it is less likely that a child has a neuroblastoma or an adult has a pheochromocytoma, but it cannot be ruled out. The tumors do not necessarily produce catecholamines at a constant rate, so increases in the hormones and metabolites will fluctuate in the urine and may not be increased in the sample tested. This is especially true when a single random urine sample is tested.
The amount of VMA produced does not necessarily correspond to the size of the tumor. This is a physical characteristic of the tumor tissue. The total amount of VMA produced will tend to increase, however, as the tumor increases in size.
A doctor will sometimes evaluate a VMA-to-HVA ratio with a neuroblastoma. A low ratio is associated with a poorer prognosis.
A variety of medications can interfere with VMA testing, but those being tested should always consult with their doctor before discontinuing any prescribed medications. Some of the drugs that can interfere include appetite suppressants, caffeine, clonidine, disulfiram, histamine, imipramine, insulin, epinephrine, levodopa, lithium, morphine, MAO inhibitors, nitroglycerin, and rauwolfia alkaloids. The effects of these drugs on VMA results will be different from person to person and are often not predictable.
This article was last reviewed on June 24, 2013. | This article was last modified on June 24, 2013.
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