Endocrine Abstracts

Phaeochromocytomas (PCC) are rare neuroendocrine tumours of chromaffin cells that are characterised by autonomous production of catecholamines. Fundamental to the detection and diagnosis is the biochemical confirmation of excessive catecholamine production by the measurement of plasma or urinary catecholamines and metanephrines. Recently, plasma metanephrines have been shown to provide a high diagnostic sensitivity for the detection of catecholamine secreting tumours and unlike plasma catecholamines do not appear to require strict attention to standardised sampling protocols. We have measured plasma metanephrines together with paired urinary catecholamines and fractionated metanephrines in 74 patients with a strong, clinical suspicion of PCC and 20 subjects in whom PCC was subsequently confirmed histologically (11 with sporadic tumours, 3 with familial adrenal tumours, 4 with functional paragangliomas, 2 with metastatic tumour). Urinary catecholamines/metadrenalines were measured by HPLC whilst plasma metadrenalines were determined by immunoassay. Results were compared to groups of healthy normotensive subjects, patients with essential and secondary hypertension, patients with histologically verified non-functioning adrenal masses and with a variety of other endocrine disorders. No statistical differences in plasma metanephrines levels were observed between duplicate blood samples collected by venipuncture at time 0 or after 10 minutes (P>0.53) in any patient. Plasma normetanephrine was elevated in all patients with sporadic tumours but was normal in a patient with MEN2A in contrast to an elevated plasma metanephrine level. Urinary levels were consistently normal in this patient. All 4 patients with paragangliomas displayed a noradrenergic secretory phenotype while the largest values for plasma normetanephrines was observed in the 2 patients with metastatic disease. We conclude that finding normal plasma metadrenalines in patients with equivocal urinary catecholamines effectively rules out a PCC /functional paraganglioma and is the test of choice in detecting these tumours in high-risk patients with familial syndromes.