A hair follicle test (HFT) is a forensic method used to detect the presence of drug metabolites incorporated into the hair shaft. This testing is favored over traditional methods like urine or blood analysis due to its significantly longer window of detection. The test offers employers, legal bodies, and healthcare professionals a reliable way to assess a person’s pattern of substance use over an extended period, providing a historical record of consumption.
Sample Collection Procedures
The process begins with a trained collector obtaining a sample under strict chain of custody protocols to prevent tampering or substitution. The collector typically gathers a small bundle of hair, approximately 90 to 120 strands (about 100 milligrams), from the vertex or crown of the head. This volume is securely collected to meet the minimum required amount for thorough laboratory analysis.
The hair is snipped as close to the scalp as possible, collecting only the strands above the skin rather than plucking the actual follicle. A standard sample length of 1.5 inches is collected, which corresponds directly to the typical 90-day detection window. The collector must ensure the sample is properly oriented, identifying the root end closest to the scalp, which represents the most recent period of use. If head hair is unavailable, body hair may be collected, but this method provides a less precise timeline of use. The sample is then secured in foil, sealed, and documented before being shipped to the testing facility.
The Science of Laboratory Analysis
Once the sample arrives at the laboratory, it undergoes a rigorous, two-step analytical process. The hair is first washed externally to remove any potential environmental contamination, such as residue from secondhand smoke. This step uses specific solvents to decontaminate the exterior of the hair shaft without removing the drug metabolites incorporated inside. Following decontamination, the laboratory uses chemical solvents to break down the hair’s keratin structure, a process necessary to release the trapped drug metabolites from the internal matrix.
The first step of analysis is an initial screening test, often an Enzyme-Linked Immunosorbent Assay (ELISA) or immunoassay. This rapid method quickly checks for the presence of specific drug classes above a set preliminary threshold. Because immunoassays can sometimes produce a false positive result due to cross-reactivity, any sample that screens positive must proceed to the more accurate confirmation stage.
The confirmation test uses highly sensitive and specific technology, typically Gas Chromatography/Mass Spectrometry (GC/MS) or Liquid Chromatography/Mass Spectrometry/Mass Spectrometry (LC/MS/MS). This advanced technique separates the chemical components of the extracted sample and identifies the molecular structure of the drug and its metabolites with high precision. The confirmation step is definitive, identifying the specific substance and precisely quantifying the amount present in the hair sample.
Detection Timeframes and Accuracy Factors
The 90-day window is based on the average growth rate of human head hair, which is approximately 0.5 inches (1.3 centimeters) per month. Therefore, a 1.5-inch sample provides a record of drug use spanning the three months leading up to the collection date. Drug metabolites take about seven to ten days after consumption to grow above the scalp surface and become detectable. This delay means the test cannot detect drug use that occurred in the immediate week before collection.
Variations in an individual’s hair growth rate can slightly shift the detection timeframe. For individuals with insufficient head hair, body hair can be used, but this reflects a less precise, longer detection window, sometimes up to several months. Common cosmetic treatments, like dyeing or bleaching, have been shown to have a minimal impact on the drug metabolites incorporated deep within the hair shaft. The test is resistant to attempts to defeat it, as external washing cannot remove the metabolites trapped within the hair’s core.
Understanding the Results
Test results are reported as either negative or positive, determined by whether the concentration of drug metabolites exceeds established cut-off levels. A negative result indicates that either no drugs were detected or the detected amount was below the laboratory’s minimum reporting threshold. These cut-off levels are set high enough to avoid false positives that could arise from trace environmental exposure or single, low-level use.
A positive result means the concentration of the drug or its metabolite has surpassed the confirmation cut-off level, which is measured in nanograms per milligram (ng/mg). This outcome suggests drug use within the specified detection window. The report confirms the substance was present above the established threshold but does not typically determine the exact date of use. Results are often reviewed by a Medical Review Officer (MRO), a licensed physician responsible for interpreting the report in a clinical context. The MRO may contact the individual to discuss any legitimate medical explanation, such as a valid prescription, that might account for the presence of a substance.