Precisely Wrong? Urinary Fractionated Metanephrines and Peer-Based Laboratory Proficiency Testing

摘要: Measurements of urinary fractionated metanephrines (normetanephrine and metanephrine), the O-methylated metabolites norepinephrine epinephrine, provide a sensitive test for diagnosis pheochromocytoma. We present evidence suggesting inaccurate metanephrine normetanephrine calibration by US laboratories. Metanephrines are in urine mainly as sulfate- glucuronide-conjugated produced from free actions conjugating enzymes (1). An acid hydrolysis step is usually performed to liberate conjugated metabolites. This minimizes requirements high analytical sensitivity, simplifying subsequent measurement. Urinary measured HPLC with electrochemical detection (HPLC-EC). Gas chromatography mass spectrometry (GC-MS) liquid tandem (LC-MS/MS) more recent alternatives offering sample throughput improved specificity (2)(3). Clinical laboratories participate proficiency testing programs, primarily aimed at determining agreement diagnostic results among laboratories. Identical survey samples distributed participating laboratories, stratified according methodologies. Laboratories that report deviating than certain amount mean their peer groups fail test. Until spring 2004, only source commercially available calibrators was Bio-Rad. As … aE-mail steve_binder{at}bio-rad.com