Plasma Normetanephrine Unit Converter
Plasma Normetanephrine Unit Converter
Convert plasma free normetanephrine between pg/mL, ng/L and pmol/L, and see why it is more posture-sensitive than metanephrine and points towards extra-adrenal disease.
Plasma Normetanephrine converter
Mass ⇄ molarPlasma free normetanephrine 110 pg/mL, supine sample
Formula and conversion factor
pg/mL = pmol/L ÷ 5.45852
- 5.45852
- derived from the molecular weight of normetanephrine, 183.20 Da
- ng/L
- numerically identical to pg/mL
- metanephrine
- a different molecule, 197.23 Da, with its own conversion factor — do not apply this factor to it
Worked example
Plasma free normetanephrine 110 pg/mL, supine sample
110 × 5.45852 = 600 pmol/L
= 110 ng/L
Which metabolite points where
| Predominant rise | Enzyme step | Typical source |
|---|---|---|
| Normetanephrine | Noradrenaline is not further methylated outside the adrenal medulla | Extra-adrenal paraganglioma, SDHB-related disease |
| Metanephrine | Adrenal medulla methylates noradrenaline to adrenaline via PNMT | Adrenal phaeochromocytoma |
Why normetanephrine behaves differently from metanephrine
Normetanephrine is the metabolite of noradrenaline, and it is the fraction that is raised in most extra-adrenal paragangliomas and in SDHB-related hereditary disease. A predominantly metanephrine rise, by contrast, indicates an adrenal phaeochromocytoma, because only the adrenal medulla carries the enzyme that methylates noradrenaline to adrenaline — extra-adrenal tissue cannot make that conversion, so its tumours release noradrenaline and its metabolite, normetanephrine, almost exclusively.
Normetanephrine is also considerably more posture-sensitive than metanephrine. A seated sample can read nearly twice a supine one, and this is the single commonest cause of a false-positive result for this analyte specifically — more so than for metanephrine, where the effect of posture, while still present, is smaller. Any unexpectedly raised normetanephrine should prompt a check of how the sample was taken before anything else.
The pattern of elevation also carries a genetic signal. A markedly raised normetanephrine with a normal metanephrine should prompt consideration of genetic testing, since around 40% of tumours presenting this way are hereditary, most often linked to the SDHB or SDHD genes. That combination of biochemical pattern and genetic likelihood is part of why the two metabolites are reported and interpreted separately rather than as a single combined figure.
Frequently asked questions
How do I convert plasma normetanephrine to pmol/L?
Multiply the pg/mL (or ng/L, which is numerically identical) value by 5.459. A normetanephrine of 110 pg/mL is 600 pmol/L.
Why does a raised normetanephrine suggest an extra-adrenal tumour?
Only the adrenal medulla can methylate noradrenaline to adrenaline. Extra-adrenal paragangliomas release noradrenaline and its metabolite, normetanephrine, almost exclusively, while adrenal phaeochromocytomas raise metanephrine as well.
Why is posture such a common cause of a false-positive normetanephrine?
A seated sample can read nearly twice a supine one for normetanephrine specifically, more so than for metanephrine. Resting supine for at least 30 minutes before the draw is essential before acting on a raised result.
When should genetic testing follow a raised normetanephrine?
When normetanephrine is markedly raised with a normal metanephrine. Around 40% of tumours with this pattern are hereditary, most often related to the SDHB or SDHD genes.
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References
- Lenders JWM et al. Pheochromocytoma and paraganglioma: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2014;99(6):1915–42.
- Eisenhofer G et al. Biochemical diagnosis of pheochromocytoma. Clin Chem. 2003;49(10):1739–52.