Why context means everything for hair testing and social care

Tabloid talk shows would have us believe that polygraph tests reliably inform us of the truth. The fallout from these results plays out in front of a live audience for our viewing pleasure. But in reality, lie detector tests are not dependable - a report by the American Polygraph Association found that polygraphs fail about 15% of the time.

Just as we assume Jeremy Kyle will offer us definitive proof about his guests’ shenanigans, many expect hair drug and alcohol testing to provide a concrete answer, too. Unlike polygraphs, hair testing delivers conclusive results; 99% of the time. However, the result (a yes or no as to whether there are drugs in the system of the person we test) is not the full story. The details of use and the interpretations can be less clear.

Context plays a big part in reporting. Without background information regarding the test subject, lab technicians can only document a positive or negative. But when we establish a deeper line of communication between the lab and the caseworker, a richer, more contextual report follows. With that in mind, let's take a look at how useful insights are generated with the provision of caseworker input using three typical scenarios.

The Situation: A subject has a 3cm hair sample taken at our lab. The caseworker expects a negative result and is surprised when the sample comes back positive for traces of cannabis and cocaine.

Scenario One: External contamination

The caseworker knows that the subject attended a party where drugs were being used. This information was offered freely by the subject who attended the event but did not actively use drugs. A urine test backs up the subject’s story - it came back negative for traces of cocaine and cannabis the day after the party. So why, two months later, does the hair test show a different result?

Unlike urine and saliva tests, which can only pick up traces of drugs and alcohol for a short period of time, a hair sample can provide a history of drug exposure for up to three months. Given that the subject was in the vicinity of drug use, it’s likely that their hair was contaminated at the party.

Traces of cannabis and cocaine will show up in the lab test. While in most cases external contamination can be minimised before analysis by appropriate wash protocols, it’s better if we have the context to corroborate our findings. With additional background information, our report would correlate the result with the accounted for by the subject’s attendance at the party and, depending on the results would discuss whether they did not or not actively use drugs.

Scenario Two: Drug history

The subject was, until two months ago, a heavy drug user. Since this time, they have been in recovery. This has been confirmed several times with urine tests.

But now, a hair drug test comes back positive for traces of cannabis and cocaine. Again, this is due to the fact that hair tests can pick up historical drug usage for a period of three months. Without knowing the detail behind the subject’s background, a lab report would simply detail the positive reading. With context provided, however, the report would explain that the results could have been affected by historical drug use and that there has decline in drug use - a positive for the person in question.

Scenario Three: Lab criteria

The results from Cansford are positive, but another lab provided a hair test result that was negative.

The likely reason for this is that, depending on their procedures, different labs use different criteria for interpreting test results. Although the numerical result could be similar or, indeed, the same, the final interpretation may be different because the cut-offs used by the two labs might be different.

To ensure the integrity of the result, the use of consistent cut-off levels between different laboratories should be observed. Suggested cut-off levels are published by scientific organisations such as the Society of Hair Testing (SoHT) and The European Workplace Drug Testing Society (EWDTS), and are in the public domain. As with any laboratory analysis, the overall interpretation should be reviewed by a suitably trained forensic toxicologist/reporting scientist, it is their role to explain the meaning of the result and ensure that results are reported in-line with current consensus(es).

Therefore, to ensure the consistency of hair drug testing is maintained, laboratories undertaking hair drug testing should adhere to the recommended cut-off levels, unless a contract specifically states differently. Ideally, the overall interpretation, compared to recommended cut-off levels, of a result should be consistent between different testing laboratories.

A cut-off is the point which determines whether a test result is positive or negative, and one lab’s cut-off may be more conservative, leading to a different result. Equally, if the two tests were taken days apart (for example, if the later test was ordered to provide a second opinion) the results can be conflicting. As with the previous two scenarios, additional information would enable Cansford to give context to the result.

Testing individuals for illicit drug and alcohol abuse isn’t as straightforward as many would like, regardless of the type of test used. Establishing the context that the subject is being tested in is as important as the test itself.

Testing an individual on any given day using blood, urine or oral fluid testing can detect drugs immediately and up to a few days later; good for establishing the current situation. But if the objective is to establish a history or lifestyle, a drug test with hair assessed along with the context of the subject’s drug history will contribute to generating a robust report.