|pmol/L||picomols per litre|
Plasma metanephrines measurement (Secondary care, HHSCP only)
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Screening and monitoring test for catecholamine secreting phaeochromocytomas/ paragangliomas, where a 24 hour urine collection for metanephrines is impractical, or in patients with inherited tumour syndromes where plasma metanephrines may offer superior sensitivity.
Preparation and procedure
- Consider stopping any interfering medications (see Table 1) where safe and practical for 1 week before test and advise to avoid paracetamol for 5 days prior to the test.
- Fast from midnight and avoidance of catecholamine-rich foods for preceding 3 days is advised if measurement of 3-methoxytyramine is likely to be important as a marker of dopamine secretion.
E.g. bananas, plums, pineapples, walnuts, tomatoes, avocados, aubergines, alcoholic drinks, vinegar.
- Patient should then be sitting upright for 30 minutes.
(GRI reference ranges are based on a seated population).
- Inform lab of test.
- Complete laboratory request forms for plasma metanephrines.
- Take blood: minimum of 1mL in red ETDA tubes and send to lab immediately for centrifugation and freezing within 2 hours.
- End test.
Table 1: Medications potentially interfering with plasma metanephrine analysis
|Tricyclic antidepressants||Amitriptyline, clomipramine, dosulepin|
|Selective serotonin reuptake inhibitors||Citalopram, fluoxetine, sertraline|
|Serotonin/noradrenaline reuptake inhibitors||Venlafaxine, duloxetine|
|a-adrenergic receptor blockers||Phenoxyenzamine, doxazosin, indoramin|
|b-adrenergic receptor blockers||Atenolol, labetalol, propranolol|
|Calcium-channel blockers||Amlodipine, diltiazem, nifedipine|
|Monoamine-oxidase inhibitors||Isocarboxazid, phenelzine, moclobemide|
|Stimulants/sympathomimetics||Ephedrine, amphetamine, nicotine, caffeine|
The normal reference ranges for seated samples (GRI correct of March 2022) are as follows:
- Metadrenaline < 510 picomol/L
- Normetadrenaline < 1180 picomol/L
- 3-methoxytyramine < 180 picomol/L
Values in the normal reference range do not suggest a catecholamine secreting phaeochromocytoma/paraganglioma.
Plasma metanephrines are susceptible to false positive results, typically in the borderline range (1 to 2 times the upper limit of the reference range (ULRR)) so that results in this range, while not excluding phaeochromocytoma, are more frequently false positives than genuine cases of phaeochromocytoma.
Data from Newcastle indicates that around 10% of cases of phaeochromocytoma/paraganglioma are associated with a normetanephrine or metanephrine result between 1 and 2 times the ULRR, around 15% of cases 2 to 4 times the ULRR and around 75 % of cases greater than 4 times the ULRR.