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Test ID: PMET Metanephrines, Fractionated, Free, Plasma

Reporting Name

Metanephrines, Fract., Free, P

Useful For

Screening test for presumptive diagnosis of catecholamine-secreting pheochromocytomas or paragangliomas

Specimen Type

Plasma EDTA


Specimen Required


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

Collection Container/Tube: Lavender top (EDTA)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Spin down within 2 hours of draw. Plasma must be separated from red blood cells within 2 hours of collection.


Specimen Minimum Volume

0.3 mL

Specimen Stability Information

Specimen Type Temperature Time
Plasma EDTA Frozen (preferred) 14 days
  Refrigerated  7 days

Reference Values

METANEPHRINE, FREE

<0.50 nmol/L

 

NORMETANEPHRINE, FREE

<0.90 nmol/L

Day(s) and Time(s) Performed

Monday through Saturday; 1 p.m.

Not reported on Sunday

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

83835

LOINC Code Information

Test ID Test Order Name Order LOINC Value
PMET Metanephrines, Fract., Free, P 57772-6

 

Result ID Test Result Name Result LOINC Value
10140 Normetanephrine, Free 40851-8
10139 Metanephrine, Free 49700-8

Clinical Information

Pheochromocytoma is a rare, though potentially lethal, tumor of chromaffin cells of the adrenal medulla that produces episodes of hypertension with palpitations, severe headaches, and sweating ("spells"). Patients with pheochromocytoma may also be asymptomatic and present with sustained hypertension or an incidentally discovered adrenal mass.

 

Pheochromocytomas and other tumors derived from neural crest cells (eg, paragangliomas and neuroblastomas) secrete catecholamines (epinephrine, norepinephrine, and dopamine). Metanephrine and normetanephrine (collectively referred to as metanephrines) are the 3-methoxy metabolites of epinephrine and norepinephrine, respectively. The metanephrines are stable metabolites and are cosecreted directly with catecholamines by pheochromocytomas and other neural crest tumors. This results in sustained elevations in plasma free metanephrine levels, making them more sensitive and specific than plasma catecholamines in the identification of pheochromocytoma patients.(1) Metanephrine and normetanephrine are both further metabolized to conjugated metanephrines and vanillylmandelic acid.

Interpretation

In the normal population, plasma metanephrine and normetanephrine levels are low, but in patients with pheochromocytoma or paragangliomas, the concentrations may be significantly elevated. This is due to the relatively long half-life of these compounds, ongoing secretion by the tumors and, to a lesser degree, peripheral conversion of tumor-secreted catecholamines into metanephrines.

 

Measurement of plasma free metanephrines appears to be the best test for excluding pheochromocytoma. The test's sensitivity approaches 100%, making it extremely unlikely that individuals with normal plasma metanephrine and normetanephrine levels suffer from pheochromocytoma or paraganglioma.(1,2)

 

Due to the low prevalence of pheochromocytomas and related tumors (<1:100,000), it is recommended to confirm elevated plasma free metanephrines with a second, different testing strategy in order to avoid large numbers of false-positive test results.(3) The recommended second-line test is measurement of fractionated 24-hour urinary metanephrines (METAF / Metanephrines, Fractionated, 24 Hour, Urine). In most cases this strategy will suffice in confirming or excluding the diagnosis. Occasionally, it will be necessary to extend this approach if there is a very high clinical index of suspicion or if test results are nonconclusive. In these cases, repeat plasma and urinary metanephrines testing, additional measurement of plasma or urinary catecholamines, or imaging procedures might be indicated.

 

Elevated results are reported with appropriate comments.

Clinical Reference

1. Eisenhofer G: Free or total metanephrines for diagnosis of pheochromocytoma: what is the difference? Clin Chem 2001 June;47(6):988-989

2. Lenders JW, Pacek K, Walther MM, et al: Biochemical diagnosis of pheochromocytoma: which test is best? JAMA 2002 Mar 20;287(11):1427-1434

3. Sawka AM, Jaeschke R, Singh RJ, Young WF Jr: A comparison of biochemical tests for pheochromocytoma: measurement of fractionated plasma metanephrines compared to the combination of 24-hour urinary metanephrines and catecholamines. J Clin Endocrinol Metab 2003 Feb;88(2):553-558

4. Algeciras-Schimnich A, Preissner CM, Young WF Jr, et al: Plasma chromogranin A or urine fractionated metanephrines follow-up testing improves the diagnostic accuracy of plasma fractionated metanephrines for pheochromocytoma. J Clin Endocrinol Metab Oct 16, 2007;doi:doi:10.1210/jc.2007-1354

Analytic Time

2 days

Method Name

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

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-General Request (T239)

-Oncology Test Request (T729)

Mayo Clinic Laboratories | Oncology Catalog Additional Information:

mml-endocrine-cancer