A hair sample drug test is a type of test that uses a bundle of about 40 strands of hair from the scalp, and the molecules embedded in the hair shaft, to check for drug use. A laboratory can detect various types of drugs in the hair of a drug user. Results are most accurate for drugs that have been in the user's system for four to 90 days. A hair sample drug test is one of the most effective drug tests for long term drug use.
When a hair sample drug test is performed, the laboratory technician will cut the hair closest to the root into small pieces. Typically, only the first 1.5 inch (3.81 cm) or so of hair is used for testing, which will provide a historic three month indication of drug use. The hair is soaked in a solvent to isolate the metabolites in the hair. This solution is then placed in a centrifuge, which spins the solution to separate the metabolites so they can be analyzed for drug usage.
When a person uses drugs, molecules from the drugs enter into the bloodstream and are carried up through the hair shaft. These molecules become trapped in the outside layer of the hair. As the hair grows out, the drug molecules remain trapped until the hair is cut or otherwise destroyed. The more drugs that are used, the greater amount of drug molecules will be found in the hair.
The average hair sample drug test will screen for opiates, amphetamines, methamphetamines, ecstasy, cocaine, marijuana, and PCP. There are more elaborate tests that will look for up to 12 drugs, both prescription and illegal. These will test for the previously mentioned drugs and will also look for Vicodin®, OxyContin®, Percocet®, Lorcet®/Lortab®, and Dilaudid®. These prescription drugs can be addicting, and are commonly abused.
Shampoo, hair styling products, and hair dye will typically not affect the results of the hair sample drug test. Hair from other parts of the body can be used when there is not enough hair on the head. Some drug screening companies will request hair from the armpit when a sample from the head is unobtainable.
A hair sample drug test can be done in a doctor's office and laboratory, at a hospital, or the hair sample can be mailed to a company that specializes in drug screening. Obtaining a mailing package and having an outside company perform the hair sample drug test may be more anonymous than having a family physician perform the test.