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Normetanephrine, Free, Plasma

Measures free normetanephrine, a breakdown product of norepinephrine, in a blood sample. Doctors use it to look into adrenal gland tumors.

AI-verified against cited sources. Awaiting expert reviewAlso called fNMN, P-NMNLOINC 2669-0

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What it is

Normetanephrine forms when your body breaks down norepinephrine, a stress hormone and nerve messenger. The "free" form is the part that is not attached to other molecules. Labs usually report it together with free metanephrine in a "plasma free metanephrines" test. Typical levels rise a little with age, so many labs print different upper limits for different age groups.

Why it matters

Doctors mostly order this when they are looking into rare tumors of the adrenal glands or nearby nerve tissue, called pheochromocytoma and paraganglioma. Guidelines list plasma free metanephrines as one of the first tests to use for that purpose. Normetanephrine is also the one that everyday causes raise most often, so mildly raised results usually have another explanation. How you are positioned before the draw matters: lying down for at least 20 minutes lowers the chance of a misleadingly high result.

If it’s low

Free normetanephrine below your lab's range is rarely the reason this test is ordered. Metyrosine, a medicine that blocks the body's production of adrenaline-type hormones, can lower the result.

Common causes

  • Metyrosine treatment

What can help

  • Tell your clinician about every medicine you take, including any used for adrenal conditions

If it’s high

A result above your lab's range means there is more free normetanephrine than usual in your blood. Most of it comes from norepinephrine released by nerves, so it rises more easily than metanephrine with everyday causes: sitting or standing before the draw, stress, caffeine, many medicines and sleep apnea. Isolated rises of up to two to three times the upper limit are common and often have one of these explanations. Increases of about three times the upper limit or more are rarely explained by everyday causes and are usually followed up closely. Your clinician can put your result in context.

Common causes

  • Blood drawn while sitting or standing, or without enough time lying down
  • Medicines such as tricyclic antidepressants, SNRI antidepressants (venlafaxine, duloxetine), MAO inhibitors, some antipsychotics, decongestants and stimulants
  • Caffeine, alcohol, tobacco or hard exercise before the draw
  • Obstructive sleep apnea
  • Stress or illness, including a heart attack or severe heart failure
  • Rarely, a tumor of the adrenal gland or nearby nerve tissue that makes adrenaline-type hormones

What can help

  • Ask about the lab's instructions for resting and fasting before the draw, and follow them
  • Bring a list of your medicines, supplements, caffeine and tobacco use, and mention any sleep problems, to your visit
  • Ask whether a repeat draw, lying down and fasting, would help put the number in context

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

Children and teens 3 ranges
  • Men, 5–11up to 165.9 pg/mL

    Source: Labcorp

  • Women, 5–11up to 148 pg/mL

    Source: Labcorp

  • 12–19up to 150.8 pg/mL

    Source: Labcorp

See Plasma free normetanephrine by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Age: upper limits rise with age at Labcorp
  • Body position: lying down for at least 20 minutes before the draw is the standard at Labcorp
  • Fasting overnight (water is fine)
  • Caffeine, alcohol, tobacco and hard exercise before the draw
  • Medicines, sleep apnea, and recent stress or illness
  • The lab: upper limits printed by Quest, Labcorp and ARUP range from 148 to 297 pg/mL
  • Sitting or standing before the draw raises norepinephrine and can push results up. Labcorp asks for at least 20 minutes lying down before and during the draw.
  • Tricyclic antidepressants, SNRI antidepressants (such as venlafaxine and duloxetine), MAO inhibitors, phenoxybenzamine, some antipsychotics, decongestants, stimulants, levodopa and cocaine can raise results.
  • Caffeine, alcohol, tobacco and strenuous exercise before the draw can raise results.
  • Obstructive sleep apnea can raise results.
  • Metyrosine treatment can lower results.
  • Samples are unstable at room temperature, so labs ask for a chilled tube and prompt separation of the plasma.

Morning, after an overnight fast and at least 20 minutes lying down Reflects your level at the time of the draw.

When to talk to a clinician

Talk with your clinician about any result your lab flags, especially one that is about three times the upper limit or higher, or if you also have repeated spells of pounding heartbeat, severe headache and sweating with high blood pressure. If you feel unwell, for example with chest pain, trouble breathing, confusion or fainting, call 911 or your local emergency number.

Questions you could ask

  • Why was this test ordered for me?
  • How should I prepare if we repeat it?
  • Was my blood drawn lying down and fasting, and could that have changed the result?
  • Could any of my medicines, caffeine, sleep problems or recent stress explain this result?
  • Would a repeat test, or a different kind of test such as a 24-hour urine collection, help put this in context?
  • Could any medicine I take lower this result?

Questions people ask

Why is my normetanephrine raised when my metanephrine is normal?

Most normetanephrine comes from norepinephrine released by nerves, so everyday things raise it more easily than metanephrine. These include certain antidepressants and other medicines, caffeine, stress, sitting up before the draw and sleep apnea. A single raised normetanephrine, especially under two to three times the upper limit, often has one of these explanations. Ask your clinician what it means for you.

Why does my lab's range depend on my age?

Normetanephrine levels rise with age, so some labs print a separate upper limit for each age group. At Labcorp it goes from 210.1 pg/mL for ages 20 to 40 up to 297.2 pg/mL above age 80. Other labs use one adult limit, so ranges differ. Use the range printed on your own report.

How do I convert pg/mL to nmol/L?

Divide pg/mL by 183.2 to get nmol/L, so 148 pg/mL is about 0.81 nmol/L. To get pmol/L, multiply pg/mL by 5.46.

Show the science and sources

Units

  • 1 pg/mL = 1 pg/mL
  • 1 pg/mL = 1 ng/L
  • 1 pg/mL = 0.005459 nmol/L
  • 1 pg/mL = 5.459 pmol/L

Open the Plasma free normetanephrine unit converter

For clinicians and researchers

Free normetanephrine is the O-methylated metabolite of norepinephrine. About 75% of it originates from norepinephrine released by sympathetic nerves rather than from the adrenal medulla, so reuptake blockers (tricyclics, SNRIs, phenoxybenzamine), atypical antipsychotics, sleep apnea and posture raise it frequently; isolated increases up to two to three times the upper limit are the most common false-positive pattern (Fagundes 2024). The Endocrine Society (2014) recommends plasma free or urinary fractionated metanephrines as the initial biochemical test for pheochromocytoma and paraganglioma. With supine sampling and matching intervals, sensitivity approaches 100% (Mayo, Labcorp). Seated sampling has been reported to keep sensitivity at 93–97% but lower specificity to about 76–85% (Fagundes 2024). Labcorp uses age-specific normetanephrine intervals (210.1 pg/mL at ages 20–40 rising to 297.2 above 80), while Quest uses a single adult limit of 148 pg/mL and also reports a free total (metanephrine plus normetanephrine) of 205 pg/mL or less. University Hospitals Birmingham lists 730 pmol/L supine and 1180 pmol/L seated. LC-MS/MS is preferred. Mayo suggests confirming a raised plasma result with a second, different strategy such as fractionated 24-hour urine metanephrines, because of the very low prevalence of these tumors.

LOINC 2669-0 (primary), 57462-4, 40851-8, 25489-6. Specimen: plasma.

Sources

  1. Metanephrines, Fractionated, Plasma Free (test 121806), Labcorp
  2. Metanephrines, Fractionated, Free, LC/MS/MS, Plasma (test 19548), Quest Diagnostics
  3. Metanephrines, Fractionated, Free, Plasma (test PMET), Mayo Clinic Laboratories
  4. Metanephrines, Plasma (Free) (test 0050184), ARUP Laboratories
  5. Metanephrines, plasma, University Hospitals Birmingham NHS Foundation Trust
  6. Pheochromocytoma and Paraganglioma: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2014)
  7. Pitfalls in the Diagnostic Evaluation of Pheochromocytomas, Journal of the Endocrine Society (2024)
  8. Normetanephrine (PubChem CID 1237), National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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