Hair follicle testing assesses an individual’s historical alcohol consumption. This analysis is often employed in legal contexts, such as child welfare or custody cases, and for employment screening or monitoring. Unlike tests for recent intake, hair testing provides a broader view of drinking patterns over an extended period.
How Hair Follicle Testing Works
Hair alcohol testing identifies specific biomarkers that the body produces when alcohol is consumed. The primary biomarkers analyzed are ethyl glucuronide (EtG) and fatty acid ethyl esters (FAEEs), including ethyl palmitate (EtPa). These metabolites are incorporated into the hair shaft through different mechanisms: EtG primarily enters the hair via sweat glands and blood circulation, while FAEEs are incorporated through the sebaceous glands that produce oil for the hair.
To perform the test, a small sample of hair, typically about 3 to 6 centimeters in length, is collected close to the scalp. Since head hair generally grows at an average rate of about 1 centimeter per month, a 3-centimeter sample can provide a detection window of approximately three months. This sample is then sent to a laboratory for analysis, where specialized techniques measure the concentrations of EtG and FAEEs present. While head hair is preferred for its consistent growth, body hair can sometimes be used, though the detection window and accuracy may vary.
Assessing Test Reliability
Hair follicle testing for alcohol reliably detects chronic heavy alcohol consumption (CHAC). It reveals patterns of significant alcohol use over time, making it suitable for historical assessment of drinking habits.
Laboratories interpret results based on established cut-off levels for EtG and FAEE concentrations, which are guided by forensic toxicology societies like the Society of Hair Testing (SoHT).
For instance, an EtG concentration of 30 picograms per milligram (pg/mg) or more in a 3-6 cm hair segment strongly indicates chronic excessive alcohol consumption. Similarly, FAEE levels, particularly ethyl palmitate (EtPa), exceeding certain thresholds (e.g., 0.35 nanograms per milligram or 350 pg/mg for a 3 cm segment) also suggest chronic heavy use. Both EtG and FAEE markers are generally recommended for a more comprehensive and accurate interpretation.
Influences on Test Outcomes
Several factors can influence the accuracy and interpretation of hair alcohol test results. External contamination from alcohol-containing products, such as hairsprays, gels, or hand sanitizers, can potentially affect FAEE levels, leading to false positives.
Hair treatments like bleaching, dyeing, perming, or straightening can also impact results. Bleaching can significantly decrease water-soluble EtG concentrations, potentially leading to false-negative outcomes. While FAEEs are more resistant to such treatments, their levels can still be partially reduced.
The extent of this impact depends on the type and aggressiveness of the treatment. Additionally, individual physiological variations, including metabolism and hair growth rate, can affect how alcohol metabolites are incorporated and retained in hair, contributing to variability in test outcomes. Laboratories often request information about hair treatments to consider these variables during result interpretation.
Scope of Hair Alcohol Testing
Hair alcohol testing identifies patterns of chronic, excessive alcohol use over an extended period, typically covering the past three months. It provides insights into an individual’s long-term drinking habits. This method is not intended to detect single drinking episodes or infrequent, moderate alcohol consumption.
Hair alcohol tests cannot determine the exact date, time, or specific quantity of alcohol consumed, nor do they indicate current alcohol impairment or intoxication. They reflect a history of consumption, providing a historical overview rather than a real-time measure of alcohol presence.