of a positive result on urine immunoassay, which is currently recommended as the first-line screening test for illicit substances [10], confirmatory testing can be done using gas chromatography/mass spectrometry (GC/MS), which is more accurate but substantially more expensive and time consuming [11]. Also, limiting some practical applications is relatively slow detection. With the exception of heavy, chronic marijuana use, the timeframe for detection of most illicit substances by either immunoassay or GC/MS is on the order of a few days [10].
