Does Lidocaine Cause False Positive Results on Cocaine Urine Drug Screen?
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Individuals who have tested positive for cocaine have claimed that lidocaine, or its primary metabolite, norlidocaine (monoethylglycinexylidide (MEGX)), have caused false positive results for the cocaine metabolite benzoylecgonine (BE) on urinary immunoassay testing.
The goal of the study was to determine if lidocaine exposure from routine medical procedures can result in false positives on a commercially available cocaine immunoassay urine drug screen (UDS).
We performed a cross-sectional observational study of patients receiving lidocaine as part of their regular care. Standard immunoassay drug screens and confirmatory liquid chromatography-mass spectrometry (LC-MS) were performed on all urine samples to assess for MEGX and BE.
In total, 168 subjects were enrolled; 121 samples positive for lidocaine were ultimately included for analysis. One hundred fourteen of the 121 were also positive for MEGX. None of the 121 were positive for cocaine/BE on the UDS (95% CI), 0–3.7% for the full sample and 0–3.9% for the 114 who tested positive for MEGX.
The present study found no evidence that lidocaine or norlidocaine are capable of producing false positive results on standard cocaine urine immunoassays.
KeywordsCocaine Lidocaine Cross-reactivity False positive Norlidocaine Urine drug screen
Author Contribution Statement
EK, BWM, DDK, and JR conceived and designed the study and obtained funding. EK, BPM, JMS, and JEC supervised the conduct of the trial and data collection. EK, BPM, JMS, and JEC undertook recruitment of patients and managed the data, including quality control. MS, JR, and DDK performed laboratory analysis on the samples. BPM, EK, and TPM provided statistical advice on the study design and analyzed the data. BPM and EK drafted the manuscript, and all authors contributed substantially to its revision. EK takes responsibility for the paper as a whole.
Sources of Funding
This study was funded by the Emory University Summer 2018 Undergraduate Research Programs Independent Research Grant.
Compliance with Ethical Standards
The manuscript was written in accordance with the Strengthening The Reporting of Observational Studies in Epidemiology (STROBE) guidelines  and the study was approved by the Institutional Review Board.
Conflicts of Interest
The view(s) expressed herein are those of the author(s) and do not reflect the official policy or position of the US Air Force Office of the Surgeon General, the Department of the Air Force, the Department of Defense, or the US Government.
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