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Test Catalog

Test ID: 3MT    
3-Methoxytyramine, 24 Hour, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

A first- and second-order screening test for the presumptive diagnosis of catecholamine-secreting pheochromocytomas and paragangliomas

 

Testing in conjunction or as an alternative to plasma metanephrines (PMET / Metanephrines, Fractionated, Free, Plasma) or plasma catecholamine (CATP / Catecholamine Fractionation, Free, Plasma) testing

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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). Dopamine secreting tumors are rarer than norepinephrine and epinephrine secreting tumors.

 

3-Methoxytyramine (3MT), metanephrine, and normetanephrine are the metabolites of dopamine, epinephrine, and norepinephrine, respectively. These metabolites are further metabolized to vanillylmandelic acid. Pheochromocytoma cells also have the ability to oxymethylate catecholamines into metanephrines that are secreted into circulation.

 

This test may be used as the first test for low-suspicion cases and also as a confirmatory study in patients with less than a 2-fold elevation in plasma free fractionated catecholamines. This is highly desirable, as the very low population incidence rate of pheochromocytoma (<1:100,000 population per year) will otherwise result in large numbers of unnecessary, costly, and sometimes risky imaging procedures.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Males: < or =306 mcg/24 hours

Females: < or =242 mcg/24 hours

Interpretation Provides information to assist in interpretation of the test results

Further clinical investigation (eg, radiographic studies) and genetic studies are warranted in patients whose 3-methoxytyramine (3MT) levels are elevated and there is a very high clinical index of suspicion.

 

Increased 3MT levels are found in patients with pheochromocytoma and dopamine-secreting tumors.

 

3MT levels of 306 mcg/24 hours or less in males and 242 mcg/24 hours or less in females can be detected in non-pheochromocytoma hypertensive patients.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test utilizes a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method and is not affected by the interfering substances that affected older spectrophotometric (Pisano reaction) methods (ie, diatrizoate, chlorpromazine, hydrazine derivatives, imipramine, monoamine oxidase [MAO] inhibitors, methyldopa, phenacetin, ephedrine, or epinephrine) or acetaminophen in high-performance liquid chromatography (HPLC) methods.

 

This method is not subject to the known interference of acetaminophen (seen with the plasma metanephrine HPLC-electrochemical detection method).

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. van Duinen N, Corssmit EPM, de Jong WHA, et al: Plasma levels of free metanephrines and 3-methoxytyramine indicate a higher number of biochemically active HNPGL than 24-h urinary excretion rates of catecholamines and metabolites Euroupean J Endocrinol 2013;169:377-382 doi: 10.1530/EJE-13-0529

2. van Duinen N, Steenvoorden D, Kema IP, et al: Increased urinary excretion of 3-methoxytyramine in patients with head and neck paragangliomas. J Clin Endocrinol Metab 2010 Jan:95(1):209-214 doi: 10.1210/jc.2009-1632

3. Kantorovich V, Pacak K; Interest of urinary dosage of 3- methoxytyramine in the diagnosis of pheochromocytoma and paraganglioma: report of 28 cases. Ann Clin Biol 2011;69(5):555-559 doi: 10.1684 /abc.2011.0612

4. Muskiet FA, Thomasson CG, Gerding AM, et al: Determination of catecholamines and their 3-o-methylated metabolites in urine by mass fragmentography with use of deuterated internal standards. Clin Chem 1979 Mar;25(3):453-460

Special Instructions Library of PDFs including pertinent information and forms related to the test