Endocrine Abstracts

First line screening for pheochromocytoma, as recommend by Endocrine Society guidelines, is to determine plasma free or urinary fractionated metanephrines. We routinely offer the latter. Although negative results rule out pheochromocytoma, it is not uncommon to see borderline results which require further investigation. In this situation we have historically relied on the measurement of plasma catecholamines in the clonidine suppression test (CST). Plasma metanephrines, however, offer a simpler and cheaper alternative. We compared results for CST with plasma metanephrine results. To date 26 patients have been investigated with urinary metanephrines, supine plasma metanephrines and CST. Results demonstrate concordance between CST and supine plasma metanephrine results when both were normal (n=17). Nine had abnormal supine plasma metanephrine results, seven of which also had abnormal CST confirming the biochemical diagnosis of pheochromocytoma. In the remaining two patients with abnormal supine plasma metanephrines one had equivocal CST (although the patient was on Imipramine, adrenal imaging was negative, and there was a low suspicion of pheochromocytoma) and the other had a normal CST, negative imaging, and pheochromocytoma was excluded. These preliminary results from 26 patients demonstrate that in the diagnosis of pheochromocytoma plasma metanephrines are an appropriate test in patients with elevated urinary metanephrines. If plasma metanephrine is normal then a CST is not required and pheochromocytoma can be excluded. For cases where supine plasma metanephrines are abnormal and diagnostic uncertainty remains then CST can be used.