Policymakers need to determine a standard cut-off, an important step in keeping drugged drivers off the road and preventing traffic accidents and fatalities.
Oral fluid testing has become a popular method for detecting the presence of illegal drugs due to its speed of collection and ease of use. This is especially the case when testing in challenging environments such as the roadside, where collecting urine and other traditional specimens for preliminary screening is not practical. Several manufacturers currently offer oral fluid screening devices either with or without an analyser. However, when it comes to THC (cannabis) screening cut-offs in oral fluid, there is great variation between the different testing devices. Policymakers should consider the current body of scientific evidence to determine a standard cut-off, an important step in keeping drugged drivers off the road and preventing traffic accidents and fatalities.
Reports show that cannabis is one of the most prevalent abused substances in driving incidents around the world.1 The use of cannabis can create a feeling of wellbeing and euphoria but can also cause more impairing effects. These include drowsiness, sedation and paranoia which, as a direct result, reduce an individual’s psychomotor skills.2
Screening at the roadside is a vital tool for detecting drivers who are under the influence of cannabis and for the prevention of traffic incidents.
A recent study showed that driving under the influence of cannabis is on the rise in the U.S. and that between 1993 and 2010, cannabis detection in drivers increased from 28.8% to 36.9%, resulting in 54.9% of drivers testing positive for cannabis alone when involved in a traffic incident. Cannabis in combination with alcohol was a factor in 25% of all incidents in which U.S. drivers had been injured in a motor vehicle accident.3 Therefore, screening at the roadside is a vital tool for detecting drivers who are under the influence of cannabis and for the prevention of traffic incidents.
However, the question of how to relate THC oral fluid concentrations to blood concentrations and subsequently set an appropriate cut-off for screening remains a widely discussed topic within the industry – and unfortunately, information in the scientific literature is limited.
Studies have shown that concentrations between 2 ng/mL and 5 ng/mL of THC in blood can result in a significant increase in impairment of the psychomotor skills and hence increase the risk of accident.4
In 2014, a study by Gjerde et. al. compared drug concentrations between whole blood and oral fluid by analysing two groups of people – volunteers and drivers who were suspected of driving under the influence of drugs. As a result of the evaluation of 182 samples, it was found that a cut-off concentration of 1 ng/mL of THC in blood is on average equivalent to a cut-off in oral fluid of 44 ng/mL. Additional research reviewed drug concentrations in drug-impaired drivers and found that THC at concentrations averaging 1.3 ng/mL in blood were similar to 39 ng/mL of THC in oral fluid.5
Oral fluid roadside screening involves the use of an antibody that targets a drug group, whereas confirmation testing is aimed at detecting one specific compound within this drug group. Therefore, the oral fluid screening cut-off must be set at a higher concentration than the blood confirmation cut-off. It is also important to note that in most countries that use preliminary screening, it is the blood confirmation results that are evidential and as such it is the cut-offs for confirmation, rather than screening, that are set in the legislation.
In conclusion, this body of research should be taken into consideration when determining a THC cut-off for an oral fluid screening device to avoid screening cut-offs that are too low for the blood confirmation cut-off for THC. This will help increase true results, avoid false positive results during the roadside testing process, and ultimately keep our roads safer.
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