Urine Total Metanephrines Unit Converter
Urine Total Metanephrines Unit Converter
Convert 24-hour urinary total metanephrines between µg/24 h, nmol/24 h and µmol/24 h, and see why the SI figure for a two-molecule mixture is a convention.
Urine Total Metanephrines converter
Mass ⇄ molar, per 24 h24-hour urinary total metanephrines 510 µg, in a normotensive woman of 25
The conversion, and why it is a convention
µmol/24 h = nmol/24 h ÷ 1,000
µg/24 h = nmol/24 h ÷ 5.07022
- 5.07022
- derived from the molecular weight of METANEPHRINE, 197.23 Da. This is the factor Labcorp’s own SI conversion table applies to urine metanephrines, and it is the same 5.07 the plasma metanephrine page uses
- 5.45852
- what the factor would be for NORMETANEPHRINE, 183.20 Da — 7.7% larger. Total metanephrines is the sum of the two, so no single factor is exact
- a convention, not an amount of substance
- the SI figure for total metanephrines assumes the whole sum has metanephrine’s molar mass, when in most patients normetanephrine is the larger fraction. Convert the fractions separately if the report gives them
Worked example
24-hour urinary total metanephrines 510 µg, in a normotensive woman of 25
510 × 5.07022 = 2,586 nmol/24 h
= 2.59 µmol/24 h
At the top of Mayo's interval for a woman of 18 to 29 (142–510 µg/24 h), and inside the interval for a woman of 70 or over (180–646)
If the same 510 µg were entirely normetanephrine the true amount would be about 2,784 nmol/24 h, 7.7% higher — which is the size of the error the single-factor convention builds in
Mayo’s 24-hour total metanephrines intervals, normotensive adults
| Group | µg/24 h | nmol/24 h |
|---|---|---|
| Female 18 – 29 | 142 – 510 | 720 – 2,586 |
| Female 70 and over | 180 – 646 | 913 – 3,275 |
| Male 18 – 29 | 190 – 583 | 963 – 2,956 |
| Male 70 and over | 246 – 753 | 1,247 – 3,818 |
| Hypertensive adults, either sex | < 1,300 | < 6,591 |
| Children 3 – 8, female | 57 – 210 | 289 – 1,065 |
| Random urine, University of Iowa | 0 – 300 µg/g creatinine | a ratio, not an excretion |
Which metanephrine test, and what each one measures
| Test | Measurand | Standing in current guidance |
|---|---|---|
| Plasma free metanephrines | Unconjugated metanephrine and normetanephrine, each reported separately | One of the two first-line tests; requires a supine sample after 30 minutes’ rest |
| Urine fractionated metanephrines | Deconjugated metanephrine and normetanephrine, each reported separately | The other first-line test; useful where supine plasma sampling is impractical |
| Urine TOTAL metanephrines (this page) | The sum of the two, deconjugated | Superseded by the fractionated assay — the sum hides which fraction is raised |
| Urine catecholamines | Adrenaline, noradrenaline, dopamine | Not recommended alone; false negatives are documented |
| Urine VMA | The terminal metabolite | Lower sensitivity than metanephrines for phaeochromocytoma |
Total metanephrines: a sum that hides the information
Phaeochromocytomas and paragangliomas leak catecholamines episodically, which is why measuring the catecholamines themselves misses tumours. What they do continuously is metabolise their own catecholamine content inside the tumour cell, by catechol-O-methyl transferase, into metanephrine from adrenaline and normetanephrine from noradrenaline. Those metabolites are produced steadily whether or not the tumour is secreting, which is the whole reason metanephrines outperform catecholamines as a screening test.
Which makes the unfractionated total an odd thing to report, because the split between the two carries real information. A predominantly adrenaline-secreting, metanephrine-rich pattern points to an adrenal phaeochromocytoma; an isolated normetanephrine rise is typical of an extra-adrenal paraganglioma and of the SDHB-related tumours that matter most for malignancy risk. Adding the two together throws that away. The Endocrine Society’s guideline recommends plasma free metanephrines or urinary fractionated metanephrines for initial testing, and Mayo and ARUP both offer the fractionated assay with the total reported alongside the fractions rather than instead of them. If you have a choice, order the fractionated test; this page exists because many reports still carry a total. For the plasma side see the plasma metanephrine converter, the plasma normetanephrine converter and the plasma metanephrines interpreter.
The conversion deserves a warning label. Metanephrine is 197.23 Da and normetanephrine 183.20, a 7.7% difference, so a sum of the two has no single molar mass. Laboratories nevertheless convert it with one: Labcorp’s SI table gives urine metanephrines as µg/24 h multiplied by 5.07, which is metanephrine’s figure applied to the whole sum. Since normetanephrine is usually the larger fraction, the convention understates the true amount of substance by up to about 7%. That is smaller than the spread of the reference interval and far smaller than a positive result, so it does not change a decision — but it is a convention rather than a measurement, and this page says so rather than printing the number as though it were exact. If your report gives the fractions, convert each with its own factor: 5.07 for metanephrine and 5.45852 for normetanephrine.
Finally, the specimen. This is a timed collection and the units have no volume in them, so an incomplete bottle manufactures a normal result; check the creatinine with the collection adequacy calculator. Where a 24-hour collection is impractical the result is reported against creatinine instead — the University of Iowa gives under 300 µg/g creatinine for adults — which is a third quantity and not convertible into either of the others without the creatinine.
Frequently asked questions
How do I convert urine total metanephrines from µg/24 h to nmol/24 h?
Multiply by 5.07022, the factor derived from metanephrine’s molecular weight of 197.23 and the one Labcorp’s SI conversion table uses for urine metanephrines. So 510 µg/24 h is about 2,586 nmol/24 h, or 2.59 µmol/24 h.
Is a single conversion factor correct for total metanephrines?
Strictly, no. Total metanephrines is metanephrine (197.23 Da) plus normetanephrine (183.20 Da), so the sum has no single molar mass and the published factor assumes metanephrine’s. Because normetanephrine is usually the larger fraction the SI figure runs up to about 7% low. It is the accepted convention, and it is small enough not to change a decision, but convert the fractions separately where the report gives them.
Should I order total metanephrines, fractionated metanephrines or the plasma test?
Not the total. The Endocrine Society recommends plasma free metanephrines or urinary fractionated metanephrines for initial testing and does not rank one above the other, though it notes a suggested slight advantage for plasma. The fractionated result tells you which metabolite is raised, which the total cannot — and an isolated normetanephrine rise points towards an extra-adrenal paraganglioma.
Does the test measure free or conjugated metanephrines?
The urine assay measures deconjugated — that is, total — metanephrines, because most urinary metanephrine is sulfate-conjugated and the specimen is hydrolysed before analysis. The plasma assay measures the free, unconjugated fraction. The two are not interchangeable and have separate reference intervals.
Why is the hypertensive reference limit so much higher?
Because hypertension itself, and several of the drugs used to treat it, raise catecholamine turnover. Mayo quotes under 1,300 µg/24 h for hypertensive adults against an upper limit of 510 to 753 µg/24 h in normotensive ones. A modest elevation in a treated hypertensive patient is therefore weak evidence; a value several times the upper limit is not.
Related calculators
References
- Mayo Clinic Laboratories. Metanephrines, fractionated, 24 hour, urine (METAF) — age- and sex-specific reference values for metanephrine, normetanephrine and total metanephrines. Test catalogue; 2026.
- 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.
- Association for Clinical Biochemistry and Laboratory Medicine. Guideline summary: phaeochromocytoma and paraganglioma (Endocrine Society 2014) — biochemical tests of choice. labmed.org.uk; accessed October 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.
- University of Iowa Health Care, Department of Pathology. Metanephrines, total — random urine, reference ranges as ug/g creatinine. Laboratory handbook; accessed October 2026.
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/