Tox Tuesday: Will the U.S. truck industry move to hair drug testing?

March 05, 2019

In the U.S., the only federally approved method for commercial driver pre-employment drug screening is to test urine samples.

This could change thanks to a proposed transportation bill that would allow trucking companies to use hair testing in addition to, or instead of, urine to meet federal requirements. Advocates for the legislation point to a few advantages to hair testing, including its longer range of detection, which they say could more effectively screen drug-using job candidates. According to CCJ Digital, one major trucking company that uses hair tests in addition to the required urine tests has turned away 5,000 candidates in the past 13 years after these candidates passed the urinalysis but failed the hair test.

The introduction of the bill is long-awaited. The U.S. Department of Health and Human Services was supposed to issue guidelines for hair testing in 2016, but did not do so. In October 2018, the department was ordered by the Opioid Response Act to provide an update on its progress in the guidelines, an update that has not yet been issued.

Advocates hope that the use of hair tests will provide better drug abuse information in the wake of the ongoing opioid crisis.

Why hair testing?

Hair tests can detect drug usage going back three months, which many see as an advantage over urine testing, which reveals the presence of drugs taken within the past few days to a week.

This is because of the way drugs enter the hair through the bloodstream. Blood carrying cells bound with the components or metabolites of a substance will enter the growing follicle, remaining in the hair when it emerges from the scalp. It takes about a week for the hair to grow past the scalp, and it continues to grow at a rate of about half an inch each month. Hair samples are typically taken from at least 1.5 inches from the head, so it takes about three months for a drug’s presence to leave the detection range.

Hair sample collection is less invasive than other methods — it can be collected under direct supervision without compromising privacy, making it easier to avoid adulteration and cheating than urine testing. Hair collection doesn’t require transportation to a medical center (as is the case with blood tests) and collection can happen as quickly as the snip of the scissors.

Once the sample is collected, it can be broken down into compounds and analyzed via several different methods, including ELISAs (enzyme-linked immunosorbent assays).


ELISAs are the best scientific method for prescreening hair samples (as well as the testing of many other samples) prior to sending for final confirmation using analytical testing. This laboratory technique works by using specific antibodies to target certain molecules (like ones associated with certain drugs). For more on how exactly this format works, check out our previous post on the science behind it. It’s also known for being an efficient and cost-effective method, especially when a large volume of samples must be tested.

When it comes to hair testing, the sensitivity levels of other assay methods, such as enzyme multiplied immunoassay technique (EMIT), are not low enough compared to ELISAs. This is especially true with complex samples such as hair that require extraction to pull drug analytes from the follicle, revealing only trace amounts of drugs in the low nanogram-per-milliliter range.

Other prescreening technologies are not capable of providing consistent detection at these low concentration levels to be reliably used for this job.

With over 100 assays available detectability of over 300 major drug analytes and metabolites, Neogen offers ELISA drug testing kits for all major drugs of abuse. See our website for more information.


Category: Toxicology, Toxicology, Toxicology