Hair follicle drug testing offers a method to detect past drug use over an extended period. This technique involves analyzing drug metabolites that become integrated into hair strands as they grow. Unlike other testing methods that capture only recent drug use, hair tests provide a broader historical record. These tests are employed across various settings to identify the presence of illegal substances or the misuse of prescription medications.
How Hair Follicle Tests Work
When drugs are ingested, they are processed by the body, and their metabolic byproducts circulate in the bloodstream. This blood supply reaches every hair follicle, feeding the growing hair cells. As new hair forms, these drug compounds and their metabolites become incorporated into the hair shaft. The hair then acts like a biological record, encapsulating these substances. Typically, a small segment of hair, usually taken close to the scalp, is collected and sent to a laboratory for analysis.
Drugs Commonly Identified
Hair follicle tests are designed to identify a range of substances and their metabolites. Among the most common categories detected are opioids, including natural and synthetic derivatives. Specific examples frequently screened for are heroin, morphine, codeine, oxycodone, hydrocodone, fentanyl, hydromorphone, oxymorphone, and methadone.
Cocaine and its metabolites like benzoylecgonine are detectable in hair samples. Amphetamines, a class of stimulant drugs, are also identified, including methamphetamine, MDMA (ecstasy), MDEA (eve), and MDA. Phencyclidine (PCP) is another substance that hair follicle tests screen for.
Marijuana, or cannabinoids, is detected by identifying THC and its metabolites, such as THC-COOH. Benzodiazepines, a class of central nervous system depressants, can also be found, including alprazolam and diazepam. Barbiturates, another type of depressant medication, are detectable. Some advanced panels may also screen for other substances like propoxyphene, meperidine, tramadol, and sufentanyl.
Detection Window and Influencing Factors
For a standard 1.5-inch hair sample collected from the scalp, drugs can typically be detected for up to 90 days. This timeframe is based on the average hair growth rate of approximately 0.5 inches (or 1 to 1.5 cm) per month.
Several factors can influence this detection window. Individual hair growth rates vary, meaning the same length of hair might represent a slightly different period for different people. The amount and frequency of drug use also play a role; heavier or more frequent use can lead to higher concentrations of substances in the hair, potentially extending the detection time. Additionally, the body’s metabolic rate can affect how quickly drugs and their metabolites are incorporated into the hair.
While external contamination is a consideration, laboratories typically employ washing procedures to differentiate between drug use and environmental exposure. Hair collected from other body areas, which often grows slower, may show a detection window extending up to 12 months.
Understanding Test Accuracy and Limitations
Hair follicle drug tests are accurate for detecting past drug use. They typically involve a two-step testing process: an initial screening, often using an enzyme-linked immunosorbent assay (ELISA), followed by confirmatory testing of any positive results with advanced methods like gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS/MS). This two-tiered approach helps to minimize the risk of false-positive results.
It is important to understand that these tests primarily detect drug use that has occurred in the past, not current impairment. Very recent drug use, typically within the last 7 to 10 days, may not be detectable because it takes time for the hair containing metabolites to grow out from the scalp. While laboratories employ rigorous washing procedures to remove external contamination, factors like hair color and cosmetic treatments (e.g., bleaching or dyeing) can sometimes influence the concentration of detected substances in the hair.