Drug screens evaluate biological samples for the presence of drugs or their metabolites. They identify specific substances or their metabolites within an individual’s system. Drug screens are used in various settings to detect illicit drugs, misused prescription medications, or performance-enhancing substances.
Substances Typically Screened
Standard drug screens target common categories of substances, often organized into “panels.” A 5-panel test, frequently used in employment screenings, checks for amphetamines, cannabinoids (marijuana), cocaine, opiates, and phencyclidine (PCP). Amphetamines include various stimulants; “MET” on a drug screen refers to methamphetamine, a potent stimulant.
Expanded panels, such as 7-panel or 10-panel tests, include additional substances. A 7-panel test adds benzodiazepines and barbiturates. A 10-panel test screens for all substances in a 5-panel test, plus barbiturates, benzodiazepines, methadone, methaqualone, and propoxyphene. Some tests may include synthetic cannabinoids (“Spice”) or synthetic cathinones (“Bath Salts”).
Opiates, also referred to as opioids, encompass a wide range of drugs, including natural opium derivatives like morphine and codeine, as well as semi-synthetic and synthetic opioids such as heroin, oxycodone, and fentanyl. Panels detect the parent drug or its metabolites, the chemical byproducts created as the body processes the substance. The specific drugs included in a panel can vary based on the test provider or the purpose of the screening.
Methods of Drug Screening
Various methods are employed for drug screening, each with distinct characteristics regarding sample collection, detection windows, and invasiveness. Urine testing is the most prevalent method, valued for its non-invasiveness and wide acceptance. Urine samples are collected at a clinic or testing facility and sent to a laboratory for analysis, providing results that indicate drug use over several days.
Hair follicle testing offers a longer detection window, identifying drug use for up to 90 days prior to the test. This method involves collecting a small hair sample, usually from the scalp, which is then analyzed for drug metabolites incorporated into the hair shaft from the bloodstream. While hair testing is non-invasive and difficult to adulterate, its limitation is its inability to detect very recent drug use.
Blood testing is accurate for detecting very recent drug use, as it identifies toxins within minutes or hours of consumption. This method is more invasive than urine or hair tests, requiring a direct blood draw. Saliva, or oral fluid, testing is non-invasive and effective for detecting recent drug use within 5 to 48 hours. A swab collects saliva from the inner cheek, and results are rapid, sometimes available within minutes for on-site tests. Sweat patch testing is a less common method that provides continuous monitoring over an extended period.
Factors Influencing Detection
Several physiological and behavioral factors influence how long a substance remains detectable in the body. An individual’s metabolic rate plays a role, as faster metabolisms lead to quicker elimination of drugs and their metabolites. Age, body weight, and overall health, including kidney and liver function, can affect metabolism and, consequently, detection times.
The dosage and frequency of substance use also impact detection windows. Higher doses and chronic use result in longer detection periods because more of the substance accumulates in the body. Conversely, infrequent use or lower doses may lead to shorter detection times. Hydration levels influence the concentration of substances in urine; diluted samples may reduce the likelihood of detection, potentially leading to false negatives.
Some substances, like THC (marijuana), are fat-soluble and can be stored in the body’s fat cells, extending their detection window, especially in individuals with higher body fat percentages. The specific properties of the substance, including its half-life and whether the test targets the parent drug or its metabolites, also determine how long it remains detectable.
Interpreting Drug Screen Results
Drug screen results are reported as either “positive” or “negative.” A positive result indicates that a substance or its metabolite was detected at a concentration equal to or above a predetermined “cut-off level.” Cut-off levels are established thresholds designed to distinguish between actual substance use and incidental exposure or environmental contamination. If the concentration falls below this threshold, the result is reported as negative, even if trace amounts of a substance are present.
False positives and false negatives can occur. False positives, where a test incorrectly indicates drug use, can be caused by certain medications, dietary supplements, or even some foods. For example, some over-the-counter cold medications, antidepressants, or antibiotics can cross-react with immunoassay tests, leading to a false positive for amphetamines or opiates. Poppy seeds can also cause false positives for opioids.
Conversely, false negatives, where a test fails to detect drug use, can result from diluted samples or attempts to adulterate the specimen. To ensure accuracy, especially for initial positive screenings, a confirmation test is performed. Gas Chromatography/Mass Spectrometry (GC-MS) is considered the “gold standard” for confirmation testing due to its specificity and accuracy, eliminating false positives by precisely identifying and quantifying substances.