To help diagnose or rule out a neuroblastoma and to monitor the effectiveness of treatment
Vanillylmandelic Acid (VMA)
When your child has symptoms consistent with neuroblastoma
Though the test is affected by caffeine and certain drugs this is not usually relevant in children.
Vanillylmandelic acid (VMA) is one of the metabolites of the catecholamines adrenaline (epinephrine) and noradrenaline (norepinephrine), hormones produced in the adrenal glands. This test measures the amount of VMA that is excreted into the urine, typically over a 24-hour period, to detect excess catecholamine production.
Neuroblastomas can produce large amounts of catecholamines resulting in greatly increased concentrations of the hormones and their metabolites.Neuroblastomas are the second most common solid tumour in childhood after brain cancer. Up to 90 per cent of cases occur in children under the age of five. Once detected, many neuroblastomas can be successfully treated.
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 collected into a container and saved. It is important that the sample be refrigerated during this time period. A single urine sample is collected for a random urine test.
Is any test preparation needed to ensure the quality of the sample?
This test is affected by caffeine, certain drugs, and stresses. Though this is less likely in children it is important to inform your healthcare professional of any medications being given, including herbal supplements and over-the-counter products, and to follow any instructions provided for things to withhold before sample collection.
How is it used?
When is it requested?
What does the test result mean?
Since the VMA test is sensitive to many outside influences false positives may be seen. When a person has large amounts of VMA in the urine it is an indication that further investigation is necessary.
If a child is being treated for a neuroblastoma, then decreasing VMA concentrations indicate a response to treatment. If a VMA concentration is initially normal and then increases in a person who has had a previous neuroblastoma, then it is likely that the tumour is recurring.
About 90% of children with a neuroblastoma will produce excess VMA and homovanillic acid. Therefore a normal result makes a neuroblastoma less likely, but it cannot be ruled out.
Is there anything else I should know?
The amount of VMA produced does not necessarily correspond to the size of the tumour. The total amount of VMA produced will tend to increase, however, as the tumour increases in size.
A variety of medications can interfere with VMA testing, including insulin but please discuss this with the doctor before withholding any medications.
Why do I have to collect my urine for 24 hours?
The reason that you need to collect the urine over a 24-hour period is because the amount of VMA excreted in the urine changes during the course of a day. By collecting all urine for 24 hours, the amount of VMA measured can be averaged over the entire day and will give a better indication of whether levels are increased or not.
Can this test be done at my doctor's surgery?
No, this test requires specialised equipment and must be performed in a laboratory. Not every laboratory will perform this assay; in some cases, your sample will need to be sent to a reference laboratory.