Sebastiano Barco1, Maria Giannina Alpigiani2, Gian Marco Ghiggeri3, Marina Talio1, Angelo Maffia1, Gino Tripodi1, Giuliana Cangemi4. 1. U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy. 2. Clinica Pediatrica, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy. 3. U.O. Nefrologia e Dialisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy. 4. U.O. Laboratorio Centrale di Analisi, Istituto Giannina Gaslini, Via Gerolamo Gaslini 5, 16147 Genova, Italy. Electronic address: giulianacangemi@ospedale-gaslini.ge.it.
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. DESIGN AND 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. CONCLUSION: 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.
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. DESIGN AND 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. CONCLUSION: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.