Drugs in the Body
What we take into our bodies often stays in our bodies for a relatively long time. That goes for certain types of illicit drugs. Although the hair itself is not alive, the follicle that produces it is. If drugs such as heroin, cocaine, methamphetamine, marijuana or alcohol are in the body, the hair follicle deposits traces of these drugs or their metabolites that act as markers of existence of drugs in the body into the hair it produces. Therefore, hair acts as a signature for drug use as long as the hair continues to exist.
Advantages
Because hair continues to grow over time, samples can provide a greater window of detection of drug use from weeks or even months in the past. Hair--unlike urine, saliva or blood--is very stable, easily transported, processed and stored, and it's hard to adulterate. It can also be used to identify chronic drug use. Hair sampling is a non-invasive method of collection.
Disadvantages
Hair drug testing has some limitations. It's not accurate enough to detect use on a specific day. Because the hair that has not yet emerged can't be tested, it can't test for very recent drug use. Also, chemical coloring of hair for cosmetic reasons can remove trace drug amounts, rendering the test ineffective.
Obtaining and Preparing a Specimen
A specimen of hair is collected by removing approximately 50 hairs. The hair is then washed to remove any dirt or chemicals for shampoos or other treatments--or contaminants such as tobacco--that may hinder the outcome of the test. The melanin within the hair is then processed out.
ELISA Testing
Samples are then screened using a technique called enzyme-labeled immunosorbent assay or ELISA. The ELISA test detects traces of drugs and their metabolites by mixing a number of types of special antibodies with the sample. Each type of antibody can bond to a different drug or its metabolites. Automated equipment is then used to detect for this bonding to identify the specific drugs in the hair sample.
GC/MS Testing
In the event the ELISA test is positive, further testing may be carried out. A gas chromatography/mass spectrometry test may be run to further identify specific markers in the hair. This secondary testing is often used to guard against false positives. The specimen is purified first, using the gas chromatograph. The full spectrum of chemical constituents in the specimen is then identified by the mass spectrometer. Spikes within the spectrum of chemicals identify specific signatures indicating specific drugs within the sample.
