While hair tests are usually used as a secondary test or in cases of criminal offenses, there is a growing number of schools and businesses that are using hair tests instead of urine tests. If the method is hair testing, it is much more likely that a nonuser will test positive, especially if the test subject is a person of color. Just walking through a room where there is marijuana smoke could result in a positive hair test. Coarser hair absorbs and maintains the tell-tale signs much more than fine hair.
The accuracy of a given drug test is determined by:
- The technology used in the test (accuracy varies considerably among types of tests)
- The chemical nature of individual drugs (varies considerably from drug to drug)
- The skills and abilities of the testing organization.
- The procedures used to ensure proper handling and processing of samples.