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
A 24-hour urine sample is preferred; sometimes a random urine sample is acceptable
Though the test is affected by caffeine and certain drugs this is not usually relevant in children.
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How is it used?
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When is it requested?
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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.
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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.
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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.
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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.