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Hair Follicle Screening
Hair testing is considered accurate and can go back as far as 90 days, As hair grows out, any drugs used are encased in the hair shaft. Longer hair can reveal an individual's drug history spanning a longer period than shorter hair. Human hair grows an average of 0.5 inches/month, which corresponds to 30 days of possible drug testing for approximately every half-inch. Testing laboratories generally require between 0.5 and 1.5 inches for testing. This represents approximately 30 to 90 days of drug use. The standard for hair 1.5 inches or longer is 80 strand or 120 if only 0.5 inches as it is by picogram weight that the hair is uniformly tested.
Some people attempt to circumvent this through shaving their heads. This does not usually work. In the absence of the required amount of hair on the scalp, body hair can be used as an acceptable substitute in the order of face, chest, arm pit, and on some occasions the police use leg hair that has a shorter slower growth rate.
It costs more than urine testing, and one must have a lab for results. Hair testing is becoming more reliable as technology advances, and there is no known way to adulterate a hair specimen in order to falsify the results of the test.
The standard hair 5 drug test includes: