Quantitative determination of free plasma metanephrines for diagnosis of catecholamine-secreting tumours. Performed by LC-MS/MS.
This method measures three O-methylated catecholamine metabolites in plasma for the biochemical diagnosis and exclusion of phaeochromocytoma and paraganglioma.
Clinical indications include:
| Analyte / Group | Components | Clinical Significance |
|---|---|---|
| Metanephrine | MN | O-methylated metabolite of adrenaline (epinephrine) |
| Normetanephrine | NMN | O-methylated metabolite of noradrenaline (norepinephrine) |
| 3-Methoxytyramine | 3-MT | O-methylated metabolite of dopamine; marker of dopamine-secreting tumours |
Plasma free metanephrines have the highest sensitivity (96–100%) of any biochemical test for phaeochromocytoma, making them the recommended first-line test.
Metanephrines are produced by the continuous intratumoral metabolism of catecholamines by catechol-O-methyltransferase (COMT). Unlike catecholamines themselves, which are released episodically, metanephrines are produced continuously by tumour tissue, providing a more reliable biochemical marker.
Sensitivity for phaeochromocytoma detection
Covering adrenaline, noradrenaline, and dopamine pathways
Recommended first-line biochemical test by Endocrine Society
Phaeochromocytomas and paragangliomas (PPGLs) are rare catecholamine-secreting tumours with potentially life-threatening consequences including hypertensive crisis, stroke, and myocardial infarction. Early biochemical detection is critical, as surgical resection is curative in the majority of cases.
The inclusion of 3-methoxytyramine extends diagnostic coverage to dopamine-secreting tumours, which may present without the classic hypertensive symptoms and can be missed by tests measuring only metanephrine and normetanephrine.
Plasma free metanephrines are measured by isotope-dilution LC-MS/MS following solid-phase extraction. This approach provides the specificity necessary to avoid false positives from interfering substances and medications, which is a significant limitation of immunoassay-based methods.
Blood should be drawn after 20–30 minutes of supine rest to minimise sympathetic activation-related false elevations. Medications known to interfere (tricyclic antidepressants, MAO inhibitors) should be noted on the request form.
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