A hair follicle test detects substances in a person’s system over an extended period by analyzing drug metabolites embedded in the hair shaft. Unlike other testing methods, hair testing offers a broader detection window. It is commonly employed in various settings, including employment screening, legal investigations, and medical evaluations.
Specific Hair Requirements
A precise amount of hair is needed for accurate laboratory analysis. Typically, a sample of about 100 milligrams of hair is required, which translates to approximately 90 to 120 individual strands. To visualize this quantity, the collected hair bundle should be roughly the thickness of a standard pencil. The hair sample must be at least 1.5 inches long, measured from the root end. This specific length and quantity are necessary for laboratories to have sufficient material.
Collection Sites and Procedures
Hair samples for testing are primarily collected from the scalp. If scalp hair is too short, unavailable, or insufficient, body hair from areas like the chest, underarm, or legs may be collected as an alternative. The collection process involves cutting the hair as close to the scalp as possible using scissors. This procedure is usually performed by a trained professional who wears gloves to prevent contamination of the sample. Proper collection ensures sample integrity and accurate test results.
Detection Window and Sample Length
The length of the hair sample directly relates to the test’s detection window, as head hair grows at an approximate average rate of 0.5 inches per month. Therefore, a standard 1.5-inch hair sample can typically provide a historical record of substance use for up to 90 days. Drugs and their metabolites enter the hair shaft through the bloodstream, as well as through sweat and oil glands on the scalp, becoming incorporated into the growing hair. It is important to note that the test analyzes the hair strand itself, not the hair follicle located beneath the skin. There is also a short delay, typically 5 to 10 days, before substances can be detected in the hair above the scalp.
Factors Impacting Sample Validity
Several factors can influence the validity and accuracy of hair follicle test results, including hair treatments such as dyeing, bleaching, perming, or straightening, which can reduce the concentration of drug metabolites detected in the hair. Additionally, external environmental contamination, such as exposure to secondhand smoke containing drug particles, can potentially lead to a positive test result, even without direct substance use. Laboratories often wash hair samples before analysis to minimize the impact of external contamination. Insufficient sample size can also compromise the test, potentially leading to an inconclusive or rejected result. The natural color of hair can also play a role, as certain drug metabolites may bind more readily to melanin.