Hair Drug Testing

Abstract

The rationale for drug analysis in hair is that drugs circulating in the bloodstream will be incorporated into the hair cells when they are formed, trapped when they are keratinized, and subsequently moved further out from the scalp as new hair is formed. In theory, the hair will form a calendar of previous drug use. Drugs are deposited in the hair through active or passive diffusion from the blood vessels in the dermal papilla, through diffusion from sweat and other secretions into the growing or mature hair, or through external drugs from vapor or solids that diffuse into the mature hair. Head hair is the dominant matrix even though alternative collection sites may be tested. The recommendation is to obtain samples from the posterior vertex which has the most consistent growth rate. Hair has been used in investigations of drug-related deaths, drug-facilitated crimes, and child protection cases. It has also been used in the monitoring of drug abuse in rehabilitation programs, the workplace, and driver’s license reinstatement. This chapter will provide an overview into the basic features of drug deposition into the hair, the analysis, and the interpretation of results.