A hair follicle drug test checks for the use of illicit substances or alcohol through the hair strands. This option provides healthcare providers to evaluate a person’s substance use history. It is because hair can deposit drugs or their metabolites up to 90 days preceding the test. However, with the rate of hair growth, it cannot detect substances within the last 7 to days of drug use. For current detection, you may use urine, oral fluid, or blood sampling.

A hair test is valuable in forensics testing to determine a person’s long-term behaviour. It is also non-invasive and has an easy sample collection procedure. However, it is less common than urine or oral fluid testing because it is more expensive and complicated to analyse. Nevertheless, its uses have been increasing as it is useful in monitoring substance abuse. The sections below present how a hair test detects drugs, the testing process, and the factors determining the result.

How Hair Follicle Drug Tests Detect Substances

Drugs and other substances are absorbed into the bloodstream after ingestion. Then, it distributes the substances to several organs like the lungs, brain, and liver. Small portions may enter the hair follicle connected to a blood vessel. Therefore, metabolites or trace amounts of the parent drug remain in the hair as it grows. A hair follicle drug test can detect substances one week after the initial exposure, depending on the hair growth.

Once the hair grows, the detection range can extend up to 90 days for accurate analysis. Moreover, the extent of drugs in the hair depends on the drug dose, colour, and texture of the hair. However, damaged hair or chemical treatments may affect the drug concentration. A hair test usually screens for cocaine, phencyclidine (PCP), amphetamines, opioids, benzodiazepines, and marijuana. Sweat and environmental exposure, such as second-hand marijuana smoke, may also integrate into the hair strands.

Head hair is typically used for a hair follicle drug test because it is the fastest growing. The hair close to the head represents the most recent drug use. A 1.5-inch hair can cover the past 90-day period. If head hair is unavailable, body hair like armpit or leg may also be used. For body hair, the detection range may be longer because of its slower growth rate.

Reasons for Testing

A hair drug test is used but not limited to the following situations:

• Pre-employment – for determining a candidate’s past use behaviour
• Randomly during employment
• Regaining a license due to a driving offence
• Probation and parole
• Divorce or child custody cases
• Drug addiction programs – monitoring usage and abstinence periods

Hair Follicle Drug Test Procedure

The hair follicle drug test process begins by cutting 100 to 200 strands of hair from the scalp. A collector would prefer the top of the head for the sample as the growth rates are more consistent than in other areas. A sufficient sample requires a minimum length of 1.5 inches of hair which can cover the past 90 days. In addition, collectors would take samples from different areas to avoid leaving a bald patch.

Collection may take place at a clinic where a lab can directly process it for analysis. Workplaces may use a hair test kit by collecting the required sample and mailing it to an accredited facility. After collection, technicians wash the specimen to remove external contaminants like shampoos and smoke before testing. The initial screening uses the ELISA method to detect illicit substances. If the result is positive, it undergoes a follow-up test.

Laboratories use gas chromatography and mass spectrometry (GC/MS) methods to examine the hair samples. The technology can detect low concentrations of drugs in hair. Furthermore, a hair follicle drug test has a turnaround time of 24 hours. Hair from different body areas may show variation because of several factors. Moreover, the results can show the patterns of substance use but not the exact time. It can also detect periods of abstinence or sobriety.

Interpreting the Results

• Negative – no illicit substances detected
• Positive – drugs reached a cut-off level to indicate a significant amount of usage. All positive tests undergo GC/MS tests to determine the type of drug used.
• Inconclusive – test results will render inconclusive for contaminated hair samples. Thus, a person must provide a new sample.

Considerations for Hair Follicle Drug Tests

Hair follicle drug testing follows strict procedures to ensure its accuracy. Several factors can play when choosing this test method. The primary of hair drug tests is their wide detection window. Workplaces or treatment facilities may use this to determine if a person is dealing with substance abuse. It can help reveal consumption patterns or habits. However, it cannot confirm recent use. Therefore, employers may consider a hair test only for specific circumstances.

Hair samples are more difficult to tamper with than urine and are easy to collect and non-intrusive than blood. Washing, dying, or using hair products will not interfere with the test results. Thus, it is hard for chronic drug users to circumvent a hair test. The test can return a positive result even if the person abstains for several days. Furthermore, the testing process undergoes two steps to avoid false positives.

Despite its accuracy, a hair follicle drug test has several limitations. Various hair growth rates can influence the time hair can show up in a drug test versus the time of the specimen collection. Additionally, they have longer processing times and are more costly. Unlike urine and oral fluid, a hair test cannot give a result at the point of collection. It needs lab testing to process the samples.

Factors Affecting Drugs in Hair

• Drug type or structure of drug compounds
• Length of hair. Body hair can be used as an alternative
• The concentration and amount of substances consumed
• Sweat
• Hair condition – damaged hair can absorb external contaminants
• Hair colour and texture – some drugs bind more to darker hair pigments
• Hair growth rates

Conclusion

A hair follicle drug test can detect illicit substances for up to 90 days from the test date. Ingested drugs break down and enter the hair shaft through the blood vessels. Once they enter the hair strands, the substance remains as the hair grows. The time it takes for drugs to show up in a hair test depends on the rate of hair growth. Most substances are identifiable in hair after seven days after the last use.

To perform the test, a collector takes a 1.5-inch length of hair near the root. Then, the specimen is analysed to detect drug usage. If the result is positive, it undergoes confirmation testing via GC/MS. Therefore, hair tests are highly accurate for drug detection over a more extended period. Furthermore, hair test results are difficult to manipulate. Shampoo and other hair products will not affect the results.