Variability amongst urine toxicology amphetamine readings with concurrent administration of fenofibrate

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.

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.