A hair follicle drug test analyzes a small hair sample to detect drug metabolites, indicating past substance use. These tests are used in contexts like employment screening and legal proceedings.
Standard Detection Period
Hair follicle drug tests typically offer a detection window of approximately 90 days. This timeframe is based on the average head hair growth rate of about 0.5 inches (1.3 centimeters) per month. To cover this period, laboratories usually require a 1.5-inch hair sample, cut from the scalp as close to the root as possible. As hair grows, drug metabolites from the bloodstream incorporate into the hair shaft, creating a chronological record of substance exposure. The hair closest to the scalp represents more recent use, while the distal end of the 1.5-inch sample reflects use from about three months prior.
Factors Influencing Detection
While a standard 90-day window exists, several factors can influence the actual detection period and test results. Individual hair growth rates vary, influenced by genetics, age, health, and hormonal levels. Faster growth might reflect a slightly shorter period for the same hair length, while slower growth could extend it.
The type and potency of the drug also play a role, as different substances metabolize and incorporate into hair at varying rates. Some drugs bind more readily to hair proteins or melanin, leading to higher concentrations and longer detectability. Additionally, the frequency and dosage of drug use influence detection; chronic or heavy use results in higher metabolite concentrations, making detection more likely and extending the detectable period. Single or infrequent use may be harder to detect or fall out of the detection window more quickly.
Hair treatments like bleaching, dyeing, perming, or straightening can impact drug concentrations. These chemical processes may damage the hair shaft, potentially reducing metabolite concentration. However, reputable laboratories account for these factors; while treatments might reduce levels, they generally do not eliminate the ability to detect past use. Labs also wash samples to remove external contamination, ensuring results reflect ingested substances.
Substances Identified
Hair follicle tests detect a range of commonly used substances. The specific panel of drugs tested depends on the individual test requirements. Common categories include amphetamines, such as methamphetamine and MDMA, and cocaine and its metabolites. Opioids, including heroin, codeine, and morphine, along with marijuana metabolites, are also frequently identified. Phencyclidine (PCP) is another substance that these tests can detect, and some tests may also screen for other substances like sedatives, stimulants, or alcohol.
Interpreting Test Findings
Hair follicle drug test results are typically reported as either negative or positive. A negative result indicates that no drug metabolites were detected, or that their presence could not be confirmed. Conversely, a positive result signifies that specific drug metabolites were found in the hair sample, providing evidence of past use within the detection window. Hair tests reveal historical drug use rather than current impairment or intoxication.
Laboratories often employ a two-step testing process: an initial screening test followed by a more specific confirmatory test if the screen is positive. This process minimizes the possibility of inaccurate results. While highly reliable, factors like environmental drug exposure or certain medications can sometimes influence results, which experts consider during interpretation.