False negative result for amphetamines on the Triage Drug of Abuse panel? The cause of the unusual phenomenon with experimental analyses.

Wakako Hikiji, Keiko Kudo, Shinji Sato, Yosuke Usumoto, Akiko Tsuji, Noriaki Ikeda

Index: Int. J. Legal Med. 123(3) , 247-52, (2009)

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Abstract

On-site drug screening devices are widely used today for their simple test procedures and instantaneous results. Among other devices, a Triage Drug of Abuse panel is considered to be highly reliable for its high specificity and sensitivity of abused drugs. Although it is known that a false positive amphetamine (AMP) result may be obtained from the urine samples containing putrefactive amines or ephedrine-related compounds, no clinical false negative methamphetamine results have been reported to date. However, a false negative Triage result was obtained from the urine of a fatal methamphetamine poisoning victim taking Vegetamine tablets. Further experimental analyses revealed that the cross-reactivity of methamphetamine and chlorpromazine metabolites, including nor-2-chlorpromazine sulfoxide, was the cause for a false negative Triage reaction for AMP. Forensic scientists and clinicians must be aware of the limitations of on-site drug testing devices and the need for the confirmatory laboratory tests for the precise identification and quantification of drugs in suspicious intoxication cases, as also recommended by the manufacturers.