Urine Vanillylmandelic Acid (VMA) Unit Converter
Urine Vanillylmandelic Acid (VMA) Unit Converter
VMA is the terminal catecholamine metabolite, now a neuroblastoma test rather than a phaeochromocytoma one. Convert mg/24 h, µg/24 h, µmol/24 h and nmol/24 h.
Urine Vanillylmandelic Acid (VMA) converter
Mass ⇄ molar, per 24 hA 24-hour urinary VMA of 7.0 mg in an adult
Formula and conversion factors
nmol/24 h = µg/24 h × 5.0461
mg/24 h = µmol/24 h ÷ 5.0461
- 198.173
- the molecular weight of vanillylmandelic acid, C9H10O5 (PubChem CID 1245; HMDB gives 198.1727)
- 5.0461
- µmol per mg. Labcorp’s own SI table gives 5.05 for VMA, which is this number to three figures — an independent check on the molecular weight
- mg/g creatinine
- how paediatric VMA is reported, because a 24-hour collection from an infant is impractical. A ratio, not an excretion, and not convertible into one without the creatinine
Worked example
A 24-hour urinary VMA of 7.0 mg in an adult
7.0 × 5.0461 = 35.3 µmol/24 h
= 35,323 nmol/24 h
At ARUP's adult upper limit of 7.0 mg/day, and below Mayo's of 8.0 mg/24 h
A normal VMA is weak reassurance against phaeochromocytoma: metanephrines are the test with the sensitivity
Urine VMA: the published limits
| Source | Limit | Unit |
|---|---|---|
| ARUP, 18 years and over | 0.0 – 7.0 | mg/day |
| The same limit in SI | 0.0 – 35.3 | µmol/day |
| Mayo VMA, 15 years and over | < 8.0 | mg/24 h |
| The same limit in SI | < 40.4 | µmol/24 h |
| ARUP, ratio to creatinine, adult | 0 – 6 | mg/g creatinine |
| ARUP, ratio to creatinine, 6 – 17 years | 0 – 9 | mg/g creatinine |
| ARUP, ratio to creatinine, 0 – 2 years | 0 – 27 | mg/g creatinine |
| Mayo, under 1 year | < 25.0 | mg/g creatinine |
What VMA is and is not the test for
| Question | Is VMA the test? | What to use instead |
|---|---|---|
| Phaeochromocytoma or paraganglioma | No — documented false negatives | Plasma free metanephrines or urinary fractionated metanephrines |
| Neuroblastoma, diagnosis | Yes, with HVA — raised in at least 90% of patients | VMA and HVA together, usually on a spot urine against creatinine |
| Neuroblastoma, monitoring | Yes | Serial VMA and HVA, same specimen type each time |
| Carcinoid or other neuroendocrine tumour | No | 5-HIAA, chromogranin A |
| Dopamine-secreting tumour | No — VMA is downstream of adrenaline and noradrenaline only | HVA, the dopamine metabolite |
The metabolite that survived as a paediatric test
Adrenaline and noradrenaline are degraded by two enzymes acting in either order. Catechol-O-methyl transferase produces the metanephrines; monoamine oxidase and aldehyde dehydrogenase then take those on to vanillylmandelic acid, the terminal metabolite and the one excreted in the largest amount. For decades a 24-hour VMA was the standard phaeochromocytoma screen, for the practical reason that it was the easiest of these compounds to measure.
It is no longer the right test for that question, and the reason is informative. The metanephrines are made inside the tumour cell, continuously, from the catecholamines the tumour stores; VMA is made mostly in the liver, from catecholamines that have already been released into the circulation. A tumour that stores rather than secretes therefore raises metanephrines while leaving VMA near normal, and false negatives for urinary VMA are documented. The Endocrine Society’s guideline recommends plasma free metanephrines or urinary fractionated metanephrines for initial testing — see the urine total metanephrines converter and the plasma metanephrine converter.
Where VMA remains genuinely useful is paediatric oncology. Neuroblastoma arises from sympathetic neural crest tissue and secretes catecholamines in about 90% of cases; urinary VMA, HVA or both are raised in at least 90% of patients, and the pair is used for diagnosis and for monitoring response. The companion test is urine HVA, the dopamine metabolite, which catches the tumours that secrete dopamine preferentially and that VMA would miss. In children the result is reported against creatinine on a spot sample rather than as a 24-hour excretion, because a timed collection from an infant is not realistic — and the reference limits fall steeply with age, from 27 mg/g creatinine in the first two years to 6 mg/g in adults, mostly because creatinine excretion rises.
Two practical points. The conversion is clean: VMA is a single molecule of 198.173 Da, so mg/24 h multiplied by 5.0461 gives µmol/24 h, and Labcorp’s own SI table independently gives 5.05 — a useful check that the molecular weight on this page is right. And the specimen matters more than the arithmetic: a 24-hour excretion and a creatinine ratio are different quantities, neither convertible into the other without the urine creatinine, and an incomplete collection understates a 24-hour VMA in direct proportion to what was missed.
Frequently asked questions
How do I convert urine VMA from mg/24 h to µmol/24 h?
Multiply by 5.0461. A VMA of 7.0 mg/day is 35.3 µmol/day and 8.0 mg/day is 40.4 µmol/day. The factor comes from VMA’s molecular weight of 198.173, and Labcorp’s SI conversion table gives the same 5.05 independently.
Is VMA still used to screen for phaeochromocytoma?
It should not be first-line. Metanephrines are made inside the tumour cell and are produced whether or not it is secreting, while VMA is made largely in the liver from catecholamines already released, so a storing tumour can give a normal VMA. The Endocrine Society recommends plasma free metanephrines or urinary fractionated metanephrines instead.
What is VMA used for now?
Neuroblastoma, with HVA. Urinary VMA, HVA or both are raised in at least 90% of patients, and the pair is used both to support the diagnosis and to monitor treatment. In children the result is normally a ratio to creatinine on a spot sample rather than a 24-hour excretion.
Why are children’s VMA limits so much higher than adults’?
Because they are ratios to creatinine, and small children excrete much less creatinine. ARUP gives 0 to 27 mg/g creatinine for ages 0 to 2 and 0 to 6 mg/g for adults. The denominator is doing most of the work, which is also why a paediatric ratio cannot be compared with an adult 24-hour figure.
Do foods or drugs interfere with urinary VMA?
Less than the older literature suggests, now that the assay is mass spectrometric rather than colorimetric — the vanilla and banana warnings date from methods that have been superseded. Catecholaminergic drugs, levodopa, labetalol and sympathomimetics still matter, and a drug review is part of interpreting any raised result.
Related calculators
References
- ARUP Laboratories. Vanillylmandelic acid (VMA) and homovanillic acid (HVA), urine — per 24 h and ratio to creatinine. Laboratory Test Directory 3018863; 2026.
- Mayo Clinic Laboratories. Vanillylmandelic acid, 24 hour, urine (VMA) — age-specific reference values. Test catalogue, test ID 9253; 2026.
- Labcorp. SI unit conversion table — urine oxalate mg/24 h x 11.4 to umol/d; VMA mg/24 h x 5.05 to umol/d; urine metanephrines ug/24 h x 5.07 to nmol/d. Test menu resources; 2026.
- PubChem. Vanillylmandelic acid, CID 1245. National Library of Medicine; accessed October 2026.
- Human Metabolome Database. Vanillylmandelic acid, HMDB0000291 — average mass 198.1727.
- Neuroblastoma. MSD Manual, Professional Edition; accessed October 2026. Urinary VMA, HVA or both are raised in at least 90% of patients.
- Lenders JWM, Duh QY, Eisenhofer G, et al. Pheochromocytoma and paraganglioma: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2014;99(6):1915–42.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/