Metanephrines (Plasma Free)

Although rare, identification of the catecholamine-producing tumours phaeochromocytoma and paraganglioma is important, as both are potentially curable. Classical symptoms of catecholamine excess encompass episodes of hypertension, severe headache and sweating, although many patients may be asymptomatic with the tumour detected incidentally. Traditionally, measurement of the hormones adrenaline and noradrenaline in timed urine collections was the first line investigation. However, repeated studies demonstrate that measurement of the O-methylated metabolites metadrenaline (metanephrine) and normetadrenaline (normetanephrine) is superior diagnostically. These metabolites offer added sensitivity for tumour detection, being produced at a constant rate, whereas excretion of the active hormones can be episodic. Plasma free metanephrines measurement appears to be the best test to exclude the diagnosis of phaeochromocytoma and paraganglioma, with a test sensitivity approaching 100%.