Drug Testing, Forensic Addictions, and Ethics

Matrices

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  Urine: Urine drug screening (UDS) utilizes antibody immunoassays that react to various drugs. The detection period varies based on the drug and its metabolism, ranging from 1 day to 1 month (e.g., for cannabis). The most basic UDS test is known as SAMHSA-5 assays for amphetamines, cocaine, marijuana, opiates, and phencyclidine and is used by the Department of Transportation and other federal agencies. UDS testing is typically expanded in clinical settings to include various other substances, including benzodiazepines, barbiturates, or synthetic opioids. Any positive test on a UDS should be sent to GC-MS confirmation testing. UDS uses cut-off values for screening that are typically higher than the cut-off values used for confirmation testing. UDS results are qualitative, showing whether the individual tested positive (above the cut-off value) or negative for a given drug. GC-MS confirmation results are both qualitative and quantitative, showing the metabolite concentration tested in the urine. Quantitative results should never be used to assess drug use frequency given the significant variability in urine-specific gravity and electrolyte content.

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  Hair: Hair drug testing can demonstrate drug use with a detection period of up to 4 or 5 months. Testing results are both qualitative and quantitative, showing the metabolite concentration tested in hair. Unlike urine testing, quantitative results obtained from hair testing can distinguish between light, moderate, and heavy drug use. Compared to urine testing, hair testing is more expensive, takes longer for results to become available, and may miss recent drug use.

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  Saliva and nails: Drug testing using saliva or nails as testing matrices are available. However, their results are not as validated and clinically useful as urine or hair testing.

Drug Testing, Drug Metabolism, and False Positives

When reading a drug testing report, it is important to understand the specific compounds tested in a given immunoassay. For example, in the SAMHSA-5 assays, the “opiates” immunoassay uses antibodies specific for morphine metabolites and, as such, detects the presence of natural and some semisynthetic opioids such as heroin, morphine, and codeine ( Fig. 12.1 , top panel). Detecting synthetic opioids such as tramadol, hydrocodone, oxycodone, buprenorphine, or fentanyl requires an extended opioid panel ( Fig. 12.1 , bottom panel). Similarly, benzodiazepine immunoassays use antibodies specific for oxazepam and detect the presence of benzodiazepines that can be metabolized into oxazepam, including diazepam, chlordiazepoxide, clorazepate, and temazepam ( Fig. 12.2 , top panel). Detecting the presence of clonazepam, alprazolam or lorazepam typically requires an extended benzodiazepine panel ( Fig. 12.2 , bottom panel). Cocaine immunoassays detect the presence of its metabolite, benzoylecgonine.

The specific substance’s pharmacokinetics determines the detection period during which an individual would be expected to test positive in a UDS. Table 12.1 lists the detection periods for commonly tested substances.