“I haven’t smoked cannabis myself, but I was in a room full of smokers!” This is a claim we have all probably heard, so how can hair testing tell the difference?
When donors are instructed to undergo hair testing for drugs, we are sometimes met with the declaration that they don’t smoke cannabis themselves, but they have been in environments where other people are smoking it. In this blog we will discuss how we can determine whether the detection of cannabis compounds in a hair sample is due to consumption or external contamination.
External contamination is when environmental factors such as heavy smoke comes into contact with a person’s hair resulting in the deposition on the hair surface of THC, the psychoactive compound in cannabis. To ensure we are testing for evidence of the consumption of cannabis, Cellmark’s hair analysis first involves washing the hair strands to decontaminate the outside, so that the laboratory testing is focussed on what has been incorporated within the hair.
In addition, when testing hair, our scientists are looking for drug ‘metabolites’. Metabolites are the biproducts of the drugs which will only be present if the drugs have been ingested (e.g. smoked) and broken down within the body. The presence of metabolites in the hair provides evidence of ingestion.
Although washing a sample of hair may not, on occasion, remove 100% of a drug (particularly after heavy contamination of the surface of the hair), the monitoring of the washes may allow the discrimination between the active direct use of a drug and environmental exposure. Washes are kept by Cellmark for further analysis if requested.
Another claim sometimes heard from donors is “Someone else was smoking cannabis and I was breathing in their smoke”. This is called passive inhalation which is harder to differentiate from someone who was actively smoking cannabis. It relies on the fact that the levels of THC and its metabolites found in hair are going to be much lower than someone who is directly smoking cannabis. This is where the Society of Hair Testing guidelines come in. The cut-off levels have been set to rule out someone only smoking cannabis once, someone who rarely smokes cannabis or someone who is passively breathing in cannabis smoke. Therefore, when we report a positive result, it means it is extremely unlikely that the person was just breathing in someone else’s cannabis smoke.
Our expert witness reports present and discuss the findings of each test and provide a conclusion to help you to make the vital decisions needed in family law matters.
If you need a quote for drug and alcohol testing, you can obtain one instantly using our online quote page. Alternatively, you will get a quick response by calling one of our friendly customer service team on 0800 036 2522 who would be happy to assist you between 8.00am and 6.00pm Monday to Friday.
* THC (Delta-9-tetrahydrocannabinol) is the psychoactive compound in cannabis and is one of the chemicals tested for in a hair drug test to determine cannabis use.