Pheochromocytomas are tumors arising from chromaffin cells of
adrenal medullary or extra-adrenal paraganglionic tissue characterized
by synthesis, metabolism and secretion of cathecolamines [1]. Although
pheochromocytomas in children are rare, they represent the most common
pediatric endocrine tumor [2]. Measurement of plasma or urinary
fractionated metanephrines represents the first-line biochemical diagnosis
[3]. In children the test with the highest specificity and sensitivity
for pheochromocytoma detection is the measurement of urinary fractionated
metanephrines (metanephrine, uMN and normetanephrine,
uNMN) [4]. High performance liquid chromatography coupled to electrochemical
detection (HPLC–EC) is the most widely used technique
for uMN and uNMN measurements. Nevertheless, some HPLC–EC
methods can be subjected to interferences from drugs and their metabolites.
Interferences caused by paracetamol [5], methenamine [6] and
sulfasalazine [7] intake have been previously reported. False-positive
results may be a pitfall in the course of a diagnosis of pheochromocytoma.
In this paper we report that an analytical interference on uNMN
caused by amoxicillin occurred in two pediatric patients.