The new NIST standards, which consist of human hair segments that have been soaked in solutions containing target drugs, help validate the accuracy of test methods for detecting those drugs. The first, SRM 2379, is designed for tests of stimulants ("uppers") such as cocaine and PCP. Its companion SRM, number 2380, checks tests for depressants ("downers"), such as codeine and THC (the active ingredient in marijuana).
As new hair tissue forms in the roots, drugs and other chemicals from the bloodstream may be absorbed into and retained by the growing follicles. Hair's advantages in drug testing--when compared to using fluids such as urine--are that it can be collected more easily, is more difficult to switch or contaminate, and retains traces of drugs for at least 90 days (not just two or three). However, hair analysis generally is not applicable to the detection of drug use initiated within the past 10 days. Therefore, it may be favored as a complement to, rather than a substitute for, traditional methods.
NIST began researching the analysis of drugs in hair in 1990 and has conducted seven interlaboratory comparison exercises to see how well different methods work, and in some cases, how well different laboratories conduct such tests.