Screening test for presumptive diagnosis of catecholamine-secreting phaeochromocytomas or paragangliomas. Measurement of plasma metanephrines has been shown to be a highly sensitive test for the detection of phaeochromocytoma; a negative test result virtually rules out the diagnosis.
Pheochromocytoma is a rare, though potentially lethal, tumour of chromaffin cells of the adrenal medulla that produces episodes of hypertension with palpitations, severe headaches, and sweating. Patients with pheochromocytoma may also be asymptomatic and present with sustained hypertension or an incidentally discovered adrenal mass.
Phaeochromocytomas and other tumours derived from neural crest cells such as paragangliomas and neuroblastomas, secrete catecholamines (epinephrine, norepinephrine, and dopamine). Metanephrines are the 3-methoxy metabolites of epinephrine and norepinephrine, respectively. The metanephrines are stable metabolites in vivo and are co-secreted directly with catecholamines by phaeochromocytomas and other neural crest tumours. 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. Metanephrine and normetanephrine are both further metabolized to conjugated metanephrines and vanillylmandelic acid.
- Plasma normetanephrine: <1180 pmol/L
- Plasma metanephrine: <510 pmol/L
- Plasma 3-methoxytyramine: <180 pmol/L
NB: The reference ranges are based on a seated reference population
EDTA specimen required. Specimen must be placed on ice as soon as possible after venepuncture and transported to the laboratory within 30 minutes. This is necessary due to the instability of the metanephrines in the blood. Not adhering to this procedure can cause incorrect results to be obtained.
Approximately 2 weeks; analysis performed by Blood Sciences, Freeman Hospital, Newcastle.