How Do Drug Test Labs Test Hair?

Drug test labs test hair using a controlled process similar to how they test blood or other samples. Because the results may be used for evidentiary purposes in legal cases or for pre-employment screenings, they also follow chain of custody handling rules to ensure that the sample has not been tampered with.

Hair Follicle Drug Test Collection Procedures

Although specific procedures may vary slightly, you will most likely be required to present some form of identification when you check in for your test.

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You will be taken to an exam room and the technician will don gloves and prepare a sample collection kit which should include sanitized scissors.

The technician will then snip a small amount of hair (usually about 100 – 200 strands of hair) from just below the crown of your head. The technician will try to obtain a sample from as close to the scalp as possible.

The hair will be placed in a specimen collection container of some sort and the container will be placed into a sealed bag.

The technician will sign the bag and, in most cases, you will be asked to initial or sign the bag as well.

This is for chain of proof. This basically ensures that both you and the technician attest to this being your sample.

The sample will then be overnighted to a drug testing laboratory.

How Drug Test Labs Test Hair

The lab technician will inspect the sample package to make sure that proper chain of custody procedures have been followed.

They will open the sample package and remove the sample.

The hair will be snipped to 1.5 inches in length measured from the part that was closest to the scalp.

A portion of the snipped section will then be washed in a process that is designed to remove any external contaminants such as shampoos or other chemicals that may be used to alter the hair follicle drug test results. The drug testing companies claim that this will also remove any contact exposure to drugs and help prevent false positives, though there is some research which seems to indicate that contact exposure can produce positive drug test results.

Drug test labs test hair by dissolving the sample with chemicals that are designed to break the hair down. This is then run through a ELISA (enzyme-linked immunosorbent assay) screening which is able to measure for the presence and amount of various drug metabolites.

If the sample is deemed to be below the testing detection thresholds, the test is negative and the results are posted back to the requestor usually within 24 hours (though, since you are usually not the requestor, it may be days or weeks before they notify you of the results).

If the sample produces a positive result, the technicians will use another sample (they don’t use the entire amount in the first test) and perform a gas chromatography (GC) and/or mass spectrometry (MS) test which is far more accurate and precise at identifying the specific chemical/drug and amount.

If a hair sample produces a positive ELISA result, it’s almost certain that the GC/MS result will also produce a positive result. The GC/MS simply allows the drug testing lab to give a precise reading level.

Due to the additional step involved in testing, it usually takes about 72 hours for the test results to be communicated back to the requestor.

Regardless of a positive or negative result, the unused portion of your hair sample will normally be kept on file at the drug test lab for about a year before it is destroyed.