Hair drug testing is a commonly used method to detect abused drug presence and metabolites in the body. It can find drug abuse precisely with detection period of up to 90 days. Analyzing a small sample of hair can reveal the drug presence as hair strands are constantly nourished by blood that contains the drug molecules. Although hair drug testing is expensive than other methods of drug testing, it is more accurate and not invasive. A hair drug test can test commonly abused five drugs like Amphetamines, Cannabinoids, Cocaine, Opiates, and Phencyclidine (PCP).

Hair Specimen Collection
A sample of 120 strands or 60 mg of hair strands that are 1.5 inches long are required for hair drug testing. At the time of specimen collection, it should be ensured that the hair is not bleached and dyed in period of last 3 months. To have a good specimen, the hair is normally collected from crown part of head. A hair clip can be used to collect a bunch of hair strands from the crown part of the head. Hair is then cut as close as possible to the scalp to get a good length for testing. These samples are then wrapped in a foil and kept in an envelope which is later send to laboratory for analysis.

Test Procedure
Before starting the test procedure, each sample is initially weighed. The sample hair strands are then cut into very small pieces and are intermixed in order to create a uniform sample. Later the drugs are extracted from hair in liquid form, which is then screened by Enzyme-Immunoassay (EIA) technique. The drug molecules that are embedded in the hair follicle can be measured through EIA. If the results come out to be positive, another part of samples is washed, and drugs are extracted. This is then subjected to confirmation testing by Gas Chromatography and Mass Spectrometry (GC/MS). The sample will be confirmed as negative, if there are no drugs or metabolites present or the result is below the cutoff level and as positive if drugs or metabolites are present above the cutoff level.

Cut Off Values Of The Drugs
The drug cut off level is the level of drug or metabolite concentration in the specimen. Any concentration level above cut off level gives a positive result. The drugs that are tested by hair drug tests have screening cut off level and confirmation cut off level. The screening cut off level and confirmation cut off level for each commonly abused drug is different. The screening cut off levels for different drugs are as under:

Amphetamines -- 0.5 ng/mg
Cannabinoids -- 0.005 ng/mg
Cocaines -- 0.5 ng/mg
Opiates -- 0.2 ng/mg
Phencyclidine (PCP) -- 0.3 ng/mg

Hair drug testing is one of the most accurate and effective methods of finding drug abuse. Possibility of adulterating hair drug testing results with shampoos or other external chemicals is minimal.