Variability amongst urine toxicology amphetamine readings with concurrent administration of fenofibrate

Abstract

Objective: The aim of this study was to highlight that concurrent administration of the common lipid-lowering agent fenofibrate may lead to false-positive amphetamine results in often-used immunoassay-based urine drug screens. It also aimed to show that there are significant moral and clinical challenges associated with the interpretation of such results amongst psychiatric inpatients. Conclusions: It is evident that different pathology laboratories may utilise different commercial urine drug-screen immunoassays in their toxicology analysis, with variability in the test specificities. Despite the relatively high prevalence of substance misuse in the population of psychiatric inpatients, there exists a need for increased vigilance towards the possibility of false-positive amphetamine results owing to likely cross-reactivity of fenofibrate with the test reagents. In cases where there is uncertainty when correlating clinically, or where false positives are suspected, gold-standard urine-sample analysis by mass spectrometry should be considered, particularly when the consequences for patients may include restrictive measures.