Screening for cocaine metabolite fails to detect an intoxication

Testing for the presence of cocaine (COC) is common in postmortem and clinical laboratories. COC use may be detected by screening urine specimens for COC metabolite. In the forensic arena, screening positive results are confirmed by a more specific and sensitive technique, such as gas chromatography-mass spectrometry. This article reports the case of an individual who died of COC intoxication but whose immunoassay screen (EMIT) for COC metabolite was negative. Gas chromatography-mass spectrometry analysis of the urine detected benzoylecgonine (BE) at a concentration of 75 ng/mL and COC at 55 ng/mL. These concentrations explain the negative screening result since the cutoff concentration of the assay was 300 ng/mL for BE. The reported cross reactivity with COC was 25,000 ng/mL. However, heart blood concentrations of COC and BE were 18,330 and 8640 ng/mL, respectively. The results from this case provide evidence that an EMIT test alone may fail to detect COC use. Individuals utilizing results of drug screening by immunoassay must be aware of the limitations of this testing methodology.