False positive biochemical testing for pheochromocytoma caused by surreptitious catecholamine addition to urine

We report a 32-year-old male who presented with astronomical elevations of urinary dopamine and epinephrine (measured by high performance liquid chromatography) and total metanephrines (measured by a spectrophotometric assay) in the setting of hypertension, spells, and headaches. Plasma fractionated metanephrines and urinary homovanillic acid levels were within normal limits. Furthermore, on serial dilution of urine, urinary total metanephrines were found to be normal. Findings on MRI imaging from the base of the neck to the pelvis and ¹²³I-m-iodobenzylguanidine scintigraphy were normal. The patient was discovered to be surreptitiously adding exogenous epinephrine and dopamine to his urine collection bottle. This is the first reported case to describe a false positive urinary total metanephrine (measured by spectrophotometric assay) in the setting of surreptitious addition of catecholamines to urine. The likely mechanism of false positivity of the spectrophotometric assay for total metanephrines was cross-reaction with the exogenous added catecholamines.