Laboratory investigation to help elucidate the presence of pheochromocytoma or paraganglioma is always utilized. The work up includes urine testing for presence of abnormal amounts of metanephrines.
The astute clinician should always consider the possibility of a falsely elevated test in this situation. The following substances may cause an abnormally high level of metanephrines in the urine
caffeine
nicotine
calcium channel blocders
levodopa
tricyclic antidepressants
monoamine oxidase inhibitors
phenoxybenzamine
Reference
Oxford Textbook of Endocrinology and Diabetes, 3rd ed., p. 855
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