Laboratory Services

Metanephrines, Fractionated, Free, Plasma

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Updated Test Information:

Test Description
Metanephrines, Fractionated, Free, Plasma

Fractionated metanephrines +; Free Metanephrine; Metanephrines free, plasma; NMN (Normetanephrines), plasma; Normetanephrine, (NMN), free; Normetanephrines, plasma

Test ID
General Information

Useful as screening test for presumptive diagnosis of catecholamine-secreting pheochromocytomas or paragangliomas

Specimen Type

EDTA Plasma

Specimen Requirements

Lavender Top (EDTA)

Specimen Collection / Processing Instructions

  • Patient Preparation: Use of an Epi-pen within last 7 days may produce inaccurate results

  • Spin down within 2 hours of draw - plasma must be separated from red blood cells within 2 hours of collection


  • Frozen (preferred): 14 days

  • Refrigerated: 7 days

Unacceptable Specimen Conditions

Gross hemolysis


  • While most circulating metanephrines are derived directly from adrenal secretion, peripheral conversion of catecholamines makes a small contribution. Therefore, substances that increase endogenous catecholamine levels can result in borderline elevations of plasma metanephrines. These include:

    • Monamine oxidase inhibitors (MOIs-a class of antidepressants with marked effects on catecholamine levels, particularly if the patient consumes tyrosine-rich foods such as nuts, bananas, or cheese)

    • Catecholamine reuptake inhibitors including cocaine and synthetic cocaine derivatives such as many local anesthetics, some of which also are antiarrhythmic drugs (eg, lidocaine)

    • Some anesthetic gases, particularly halothane

    • Withdrawal from sedative drugs, medical or recreational, in particular alcohol, benzodiazepines (eg, Valium), opioids, and some central acting antihypertensive drugs, particularly clonidine, but, generally not cannabis or other hallucinogens such as lysergic acid diethylamide (LSD), mescal, or peyote

  • The observed elevations of plasma metanephrines are usually minor

  • We are currently not aware of any substances that interfere directly in the assay

  • Artifactually decreased plasma metanephrine levels may be observed when patients are already receiving metyrosine treatment. This drug may be administered in suspected or confirmed cases of pheochromocytoma while awaiting definitive treatment. It inhibits tyrosine hydroxylase, the enzyme that catalyzes the first step in catecholamine synthesis.


Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Estimated TAT

2-4 days

Testing Schedule


Test Includes

  • Metanephrine, Free

  • Normetanephrine, Free


14 days

CPT Code(s)


Additional Information
Minimum Sample Volume

0.3 mL

Reference Range
    • <0.50 nmol/L


    • <0.90 nmol/L
Performing Lab


LOINC Code(s)

40851-8, 49700-8