Drug Testing

Broadly defined, drug testing uses a biological sample to detect the presence or absence of a drug or its metabolites. This process can be completed in a variety of settings and with a variety of techniques. Many drug screening immunoassays were initially designed for use in the workplace as a drug screening tool for employees. As these tests have become cheaper, more readily available, and easier to use, these tests are now standard in many clinical laboratories. Despite their prevalence, many physicians and providers do not understand how these tests function and their associated limitations. Despite the drawbacks, drug testing plays an essential role in the clinical setting because clinical examination, patient self-reporting, and collateral reporting will often underestimate the actual incidence of substance use. The use of drug screens is also becoming increasingly important in the management of patients with chronic pain and in the treatment of substance use disorders.

The most commonly tested-for substances are amphetamines, cannabinoids, cocaine, opiates, and phencyclidine (PCP). These drugs are also referred to as the "NIDA five" as these were the five drugs that were recommended for drug screening of federal employees by the National Institute on Drug Abuse (NIDA). This responsibility now falls on the Substance Abuse and Mental Health Services Administration (SAMHSA). There are now expanded drug screens that include testing for oxycodone, methadone, buprenorphine, and fentanyl, among many other drugs.

There are several biological samples that can be used for testing. These include blood or serum, sweat, hair, oral fluid, nails, and urine. The most commonly used biological sample is urine, as it is non-invasive, and the concentration of a given xenobiotic is generally higher when compared to other samples. This usually results in a higher sensitivity. Additional considerations include how long a xenobiotic remains detectable in various matrices. It is important to consider these aspects in the context of why testing is being performed.

Immunoassays remain the most common and easily accessible form of testing. More advanced methods, particularly in confirmatory testing, are available and include gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS). These advanced methods tend to have higher specificity and sensitivity as compared to immunoassays, but are more expensive and require specialized equipment and training.