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Blood Test Tracker

Metanephrine, Free, Plasma

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

AI-verified against cited sources. Awaiting expert reviewAlso called fMN, P-MNLOINC 38494-1

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What it is

Metanephrine forms when your body breaks down epinephrine (adrenaline), a stress hormone made by the adrenal glands. Adrenaline itself is released in bursts, but metanephrine is made steadily, so a blood level gives a steadier picture. The "free" form is the part that is not attached to other molecules. Labs usually report it together with free normetanephrine in a "plasma free metanephrines" test.

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. How you are positioned before the draw matters: lying down for at least 20 minutes lowers the chance of a misleadingly high result. Mildly raised results are common and usually have everyday causes.

If it’s low

Free metanephrine 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 metanephrine than usual in your blood. Most mild increases are not caused by a tumor. Sitting or standing before the draw, stress, caffeine, tobacco, hard exercise and many medicines can all raise it. 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, MAO inhibitors, decongestants and stimulants
  • Caffeine, alcohol, tobacco or hard exercise before the draw
  • 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 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.

For adults: up to 88 pg/mL. Source: Labcorp, Quest Diagnostics, Mayo Clinic Laboratories, ARUP Laboratories, University Hospitals Birmingham NHS Foundation Trust.

What can affect your result

  • 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, and recent stress or illness
  • Handling: the tube is usually chilled and the plasma separated quickly
  • The lab: upper limits printed by Quest, Labcorp and ARUP range from 57 to about 97 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, MAO inhibitors, some alpha blockers, decongestants, stimulants, levodopa and cocaine can raise results.
  • Caffeine, alcohol, tobacco and strenuous exercise before the draw can raise results.
  • Metyrosine treatment can lower results.
  • Older HPLC-electrochemical methods were prone to interference, including from acetaminophen. Mayo knows of no direct interference with its LC-MS/MS method.
  • 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 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 do I need to lie down before the blood draw?

Standing or sitting makes your body release more norepinephrine, which can nudge results up and cause a misleading high. Labcorp asks you to lie flat for at least 20 minutes before and during the draw. If lying down is not possible, tell the person drawing your blood. Some labs accept a seated draw or have separate seated ranges.

Why do labs print different upper limits?

For free metanephrine the upper limit is 57 pg/mL at Quest, 88 at Labcorp and about 97 (0.49 nmol/L) at ARUP. Labs use different methods, draw positions and groups of healthy people. Use the range printed on your own report.

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

Divide pg/mL by 197.23 to get nmol/L, so 88 pg/mL is about 0.45 nmol/L. To get pmol/L, multiply pg/mL by 5.07.

Show the science and sources

Units

  • 1 pg/mL = 1 pg/mL
  • 1 pg/mL = 1 ng/L
  • 1 pg/mL = 0.00507 nmol/L
  • 1 pg/mL = 5.07 pmol/L

Open the Plasma free metanephrine unit converter

Is a change real?

Plasma free metanephrine naturally varies about 13.5% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 42% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Biological Variation of Adrenal-Related Endocrine Biomarkers Used for Investigation of Secondary Hypertension (Lerpold AS et al.).

For clinicians and researchers

Free metanephrine is the O-methylated metabolite of epinephrine, formed by catechol-O-methyltransferase in adrenal chromaffin cells and chromaffin tumor cells. The Endocrine Society (2014) recommends plasma free or urinary fractionated metanephrines as the initial biochemical test for pheochromocytoma and paraganglioma. Labcorp, citing that guideline, advises sampling supine with intervals established in the same position, and University Hospitals Birmingham gives the same advice. 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). Intervals are method- and position-specific: Labcorp uses a single metanephrine cut-off (88 pg/mL for both sexes and all ages) chosen slightly above the 99.5th percentile, University Hospitals Birmingham lists 450 pmol/L supine and 510 pmol/L seated, and Quest reports 57 pg/mL. LC-MS/MS is preferred; Mayo notes that its older HPLC-electrochemical method was prone to interferences (acetaminophen among them) and knows of no direct interference with its LC-MS/MS method. Drug interferences raise normetanephrine more often than metanephrine. 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 38494-1 (primary), 49700-8, 29141-9, 25473-0. 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. Metanephrine (PubChem CID 21100), 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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