title: Amoxicillin-associated interference in an HPLC-EC assay for urinary fractionated metanephrines: potential pitfall in pheochromocytoma biochemical diagnosis.
abstract: OBJECTIVE
  Measurement of urinary fractionated metanephrines represents a first-line test for the biochemical diagnosis of pheochromocytoma. The high performance liquid chromatography coupled to electrochemical detection (HPLC-EC) assays used in the routine clinical laboratory can be subjected to analytical interferences by the presence of drugs or their metabolites. In this paper we describe the interference on urinary normetanephrine (uNMN) caused by amoxicillin.
  
  
  METHODS
  Two pediatric patients suspected of pheochromocytoma had very high uNMN levels (2543 and 4227μg/g Cr respectively; upper reference value: 339μg/g Cr). Amoxicillin interference was assessed by comparison for co-elution with uNMN and by LC-MS/MS analysis.
  
  
  RESULTS
  After amoxicillin interference was suspected and the therapy was stopped uNMN levels returned to normal (149 and 214μg/g Cr respectively). Chromatograms obtained by HPLC-EC clearly showed that amoxicillin co-elutes with uNMN. Patients' uNMN levels measured by LC-MS/MS were in the normal range.
  
  
  CONCLUSIONS
  Amoxicillin is responsible for analytical interference on HPLC-EC assay for uNMN. This finding can be of help in distinguishing true-positive from false-positive results in the course of a biochemical diagnosis for pheochromocytoma.
authors.affiliation: U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy.
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Barco
authors.affiliation: Clinica Pediatrica, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy.
authors.forename: Maria Giannina
authors.initials: MG
authors.lastname: Alpigiani
authors.affiliation: U.O. Nefrologia e Dialisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy.
authors.forename: Gian Marco
authors.initials: GM
authors.lastname: Ghiggeri
authors.affiliation: U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Talio
authors.affiliation: U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Maffia
authors.affiliation: U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy.
authors.forename: Gino
authors.initials: G
authors.lastname: Tripodi
authors.affiliation: U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy. Electronic address: giulianacangemi@ospedale-gaslini.ge.it.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Cangemi
mesh_terms: D000293:Adolescent; D000310:Adrenal Gland Neoplasms / Q000473:pathology / Q000652:urine*; D000658:Amoxicillin / Q000008:administration & dosage* / Q000009:adverse effects / Q000652:urine; D002648:Child; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D008297:Male; D009647:Normetanephrine / Q000302:isolation & purification / Q000652:urine*; D010673:Pheochromocytoma / Q000473:pathology / Q000652:urine*; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry
chemical_list: D009647:Normetanephrine; D000658:Amoxicillin
keywords: Amoxicillin; HPLC–EC; Interference; Normetanephrine; Pheochromocytoma