Hair drug testing

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 how long does marijuana stay in your system history spanning a longer period than shorter hair. Human hair grows an average of 1.5 inches/month, which corresponds to 30 days of possible drug testing for approximately every 1.5 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 .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. If all hair is shaven, the follicles of the hair may be used in place of the hair. Hair follicle testing is normally not part of an employer-based drug testing program using hair.

Additionally for pre-employment hair testing, the inability to obtain a sample may be grounds for not hiring the individual. Hair Testing labs are regulated by CLIA or SAMHSA. There is a growing trend in major companies and law enforcement agencies to utilize hair analysis on account of its efficiency and reputation as the gold standard when considering test accuracy. This technology makes use of radioimmunoassay or the ELISA technology with subsequent confirmation by mass spectrometry.

In recent years, hair testing has been the subject of a number of lawsuits. Studies have shown that different ethnic groups have different hair structure, potentially leading to false positives.

A two-step process that opens the cuticle layer and allows deeper penetration is used. Some laboratories perform extensive wash procedures on each hair sample to eliminate the possibility of a false positive from drug residue on the outside of the hair shaft.