What Will a Hair Follicle Test Show?

Hair follicle testing, a sophisticated method of drug detection, offers a unique window into an individual’s historical substance use. Unlike urine or saliva tests, which capture recent consumption, hair analysis can reveal drug use over a much longer period, often up to 90 days or even longer depending on hair length. This extended detection window makes it a valuable tool in various screening scenarios, from employment and legal proceedings to clinical and personal use. Understanding what a hair follicle test can reveal is crucial for anyone facing such a screening or considering its application.

The Science Behind Hair Follicle Testing

The principle behind hair follicle testing is rooted in the way drugs and their metabolites are absorbed into the hair shaft. When a drug is ingested, it enters the bloodstream. From the bloodstream, drug molecules can diffuse into the dermal papilla, the actively growing part of the hair follicle. As the hair shaft grows outward, these drug molecules become permanently embedded within the keratin structure of the hair.

Drug Incorporation into Hair

The process of drug incorporation is not immediate. It typically takes several days to a week or more after consumption for drug molecules to become detectable in the hair. This lag time is due to the hair growth cycle. New hair cells are constantly being produced at the root, and as they mature and push outwards, they trap the drug metabolites. Therefore, the section of hair closest to the scalp represents the most recent drug use, while segments further down the shaft reflect earlier exposure.

Metabolism and Metabolites

Drugs are metabolized in the body by enzymes, primarily in the liver. This process breaks down the parent drug into various metabolites. Both the parent drug and its metabolites can be incorporated into the hair. The specific drug and the individual’s metabolism will determine the type and quantity of compounds found in the hair. For example, cannabis use will likely result in the detection of delta-9-tetrahydrocannabinol (THC) and its metabolite 11-nor-delta-9-THC-9-carboxylic acid (THC-COOH). Opioid use might reveal morphine, codeine, or heroin.

Factors Influencing Detection

Several factors can influence the detection of drugs in hair:

• Hair Length: Longer hair provides a longer historical record of drug use. A standard 1.5-inch hair sample, with an average hair growth rate of 0.5 inches per month, can typically cover approximately 90 days of drug use. If an individual has significantly longer hair, the detection period can be extended.
• Hair Color and Treatment: While controversial and generally considered to have minimal impact in scientifically validated tests, some studies have explored the potential influence of hair color and chemical treatments (like dyes or perms) on drug absorption. Most certified laboratories account for these variables and employ rigorous wash steps to remove external contaminants.
• External Contamination: A significant concern with hair testing is the possibility of external contamination, where drug residue from the environment adheres to the hair surface. To mitigate this, laboratories perform rigorous washing procedures on the hair sample before analysis. They also analyze for both the parent drug and its metabolites, as external contamination is less likely to result in the presence of metabolites within the hair shaft.
• Dosage and Frequency of Use: Higher doses and more frequent drug use will generally lead to higher concentrations of drugs and metabolites in the hair, making them easier to detect. Occasional or very light use might result in concentrations below the laboratory’s established cut-off levels.
• Environmental Factors: While less common, significant exposure to drug-laden environments could potentially lead to external contamination.

What Specific Substances Can Be Detected?

Hair follicle tests are highly versatile and can be used to detect a wide range of prescription medications, illicit drugs, and even certain alcohol biomarkers. The specific panel of drugs tested can be customized depending on the requirements of the screening.

Illicit Drugs

Commonly screened illicit drugs include:

• Cannabinoids: Marijuana (THC), synthetic cannabinoids.
• Opioids: Heroin, morphine, codeine, oxycodone, hydrocodone, fentanyl.
• Stimulants: Cocaine, methamphetamine, amphetamine, MDMA (ecstasy).
• Sedatives/Hypnotics: Benzodiazepines (e.g., Xanax, Valium), barbiturates.
• Hallucinogens: LSD, PCP, psilocybin mushrooms.
• Dissociative Anesthetics: Ketamine.

Prescription Medications

A significant advantage of hair testing is its ability to detect the misuse of prescription medications. This is particularly relevant in contexts where diversion or abuse of controlled substances is a concern. Some commonly tested prescription drugs include:

• Opioid Pain Relievers: Oxycodone (OxyContin, Percocet), hydrocodone (Vicodin, Lortab), codeine, morphine, fentanyl.
• Stimulant Medications: Amphetamines (Adderall, Vyvanse) used for ADHD.
• Sedative-Hypnotics: Benzodiazepines like alprazolam (Xanax), diazepam (Valium), lorazepam (Ativan).
• Other Prescription Drugs: Depending on the test panel, drugs like tramadol, meperidine, or even certain antidepressants might be included.

Alcohol Biomarkers

Beyond drug detection, hair analysis can also provide insights into chronic alcohol abuse. Ethyl glucuronide (EtG) and fatty acid ethyl esters (FAEEs) are two primary biomarkers tested for alcohol consumption.

• Ethyl Glucuronide (EtG): EtG is a direct metabolite of ethanol. It can be detected in hair for up to three months after heavy alcohol consumption. The concentration of EtG in hair is generally proportional to the amount of alcohol consumed.
• Fatty Acid Ethyl Esters (FAEEs): FAEEs are formed when ethanol reacts with fatty acids in the body. They are also incorporated into the hair shaft and can indicate chronic, heavy alcohol consumption. Common FAEEs tested include ethyl myristate, ethyl palmitate, ethyl oleate, and ethyl stearate.

The detection of these alcohol biomarkers indicates a pattern of consumption over time, rather than a single instance of drinking.

The Hair Follicle Testing Process

The process of hair follicle testing is a multi-step procedure designed to ensure accuracy and reliability.

Sample Collection

Hair samples are typically collected from the crown of the head, near the scalp. This is because hair closest to the scalp represents the most recent growth and thus the most recent drug use. If head hair is unavailable or unsuitable, body hair (e.g., from the arms, legs, or chest) can be used, although it may reflect a longer period of use due to slower growth rates. The collector will snip several small sections of hair, ensuring a sufficient quantity is obtained. The sample is then sealed and documented.

Laboratory Analysis

Once collected, the hair sample is sent to a certified laboratory for analysis. The process involves:

1. Washing: The hair is meticulously washed to remove any external contaminants. This step is critical to differentiate between ingested drugs and environmental exposure.
2. Decontamination: A more thorough decontamination process may follow the initial washing.
3. Extraction: The washed hair is then cut into small segments, and drugs are extracted from the keratin structure using specific solvents and techniques.
4. Screening (Immunoassay): The extracted sample is initially screened using highly sensitive immunoassay techniques. These tests can quickly detect the presence of a broad range of drug classes.
5. Confirmation (Mass Spectrometry): If the immunoassay screen is positive, the sample undergoes confirmatory testing using Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Mass Spectrometry (LC-MS). These methods provide definitive identification and quantification of specific drugs and their metabolites, confirming the positive result with a high degree of accuracy.

Interpretation of Results

The laboratory reports the presence or absence of specific drugs and their metabolites. Results are typically reported as positive or negative based on established cut-off levels. These cut-off levels are set to ensure that only drug use above a certain threshold is considered positive, minimizing the risk of false positives due to trace environmental exposure or passive inhalation. For alcohol biomarkers, higher concentrations typically indicate chronic or heavy consumption.

Limitations and Considerations

While hair follicle testing is a powerful tool, it’s essential to acknowledge its limitations and consider certain factors when interpreting results.

Detection Window Nuances

As mentioned, the 90-day window is an approximation based on average hair growth. If an individual has significantly slower hair growth, the detection window may be shorter for a given hair length. Conversely, individuals with very fast hair growth might have a slightly shorter window for a 1.5-inch sample.

External Contamination Mitigation

While laboratories employ rigorous washing protocols, the possibility of external contamination can never be entirely eliminated. However, the analysis of both parent drugs and their metabolites significantly reduces the likelihood of a false positive due to external factors, as metabolites are typically only formed after ingestion.

Passive Inhalation and Environmental Exposure

In rare cases, significant passive exposure to drugs (e.g., living with a heavy drug user in an unventilated space) could potentially lead to trace amounts being detected. However, the concentrations would likely be significantly lower than those resulting from direct ingestion.

Medical Explanations

Certain medical conditions or the use of certain over-the-counter medications can, in very rare instances, lead to false positive results on initial immunoassay screening. This is why confirmatory testing with mass spectrometry is a standard and crucial part of the process. It is always advisable to discuss any medications or supplements being taken with the testing administrator or laboratory.

Ethical and Legal Considerations

Hair follicle testing is often used in situations with significant legal or employment implications. It’s important for individuals to be aware of their rights and the specific policies governing such tests. The Chain of Custody is paramount to ensure the integrity of the sample from collection to analysis.

In conclusion, a hair follicle test offers a comprehensive look into an individual’s historical drug use, typically spanning the past 90 days. By detecting the presence of parent drugs and their metabolites embedded within the hair shaft, this method provides a valuable, albeit nuanced, assessment of substance consumption. Understanding the science, the process, and the inherent limitations is key to interpreting the results accurately and ethically.