A hair follicle test detects substances by analyzing a small hair sample. It reveals patterns of substance use over an extended period. When a substance is consumed, its metabolites enter the bloodstream and become incorporated into the hair as it grows. It identifies these embedded substances, providing insights into past usage.
Understanding the Detection Window
Hair follicle tests are known for their broad detection window, identifying substance use up to 90 days prior to the test. This timeframe is linked to the average growth rate of head hair, which is approximately half an inch (1.27 cm) per month. For a standard test, about 1.5 inches (3.81 cm) of hair is collected from the scalp, analyzing substance exposure over the preceding three months. The long detection period stems from how substances are incorporated into the hair shaft; once drug metabolites enter the hair, they remain trapped as the hair grows, creating a historical record of substance use. This makes hair follicle testing a reliable method for assessing chronic or long-term patterns of use.
Factors Affecting Detection
Several factors influence the detection window and substance concentration. An individual’s hair growth rate is a primary variable, with variations slightly altering the 90-day window. The specific substance also plays a role, as different drugs are metabolized and incorporated at varying rates. Frequency and dosage significantly impact detection; higher or more frequent use generally leads to greater metabolite concentrations. A person’s metabolic rate also influences how much of a substance is incorporated into the hair shaft.
The Testing Process and Result Delivery
Sample Collection
The hair follicle testing process begins with collecting a hair sample, typically from the scalp. Approximately 1.5 inches of hair is cut as close to the scalp as possible. The collection process is straightforward and non-invasive, minimizing sample adulteration.
Laboratory Analysis and Results
Once collected, the hair sample is sent to a specialized laboratory. Laboratories often employ a two-step methodology: an initial screening test followed by a confirmatory test if screening indicates substances. The confirmatory test uses advanced techniques such as gas or liquid chromatography and mass spectrometry for precise identification and quantification. The time to receive results typically ranges from a few business days to about a week, depending on the laboratory’s workload and the specific tests requested.
Reliability and Considerations
Hair follicle tests are highly reliable for detecting past substance use, largely because they are difficult to adulterate or “cheat.” Unlike some other testing methods, it is challenging for individuals to tamper with a hair sample once it has been collected. While scalp hair is most commonly used, body hair can also be tested, though it may reflect a longer detection window due to slower growth rates. Laboratories differentiate between substances incorporated into the hair from ingestion and those resulting from external contamination, such as being around drug smoke. They focus on drug metabolites that are absorbed internally.