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mobile drug testing devices
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News_
STUDY CASTS DOUBT ON ACCURACY OF MOBILE DRUG TESTING DEVICES

12 September 2019

Research at the University of Sydney Lambert Initiative for Cannabinoid
Therapeutics suggests the devices currently used return both false positives and
false negatives.


Professor Iain McGregor is the Academic Director of the Lambert Initiative.

New research conducted by the Lambert Initiative for Cannabinoid Therapeutics at
the University of Sydney calls into question the reliability of the two devices
that are currently being used for mobile drug testing (MDT) in NSW and other
Australian states. These devices were used in the prosecution of almost 10,000
cannabis users for drug driving in NSW in 2016 (the last year for which data are
available).

The study, published in the journal Drug Testing and Analysis, found that the
devices frequently failed to detect high concentrations of tetrahydrocannabinol
(THC). False negative rates were 9 percent and 16 percent for the two devices
but they also sometimes gave a positive result when saliva THC concentrations
were very low or negligible (false positive rate of 5 percent and 10 percent).

“Detecting impairment due to cannabis use is an important goal in promoting road
safety but using saliva tests to do this appears fraught with issues,” said
Professor Iain McGregor, Academic Director of the Lambert Initiative for
Cannabinoid Therapeutics and senior author of the study.

The study, led by PhD student Thomas Arkell, was part of a larger study looking
at the effects of vaporised cannabis on driving.

In the same way that breathalysers can detect whether a driver has a blood
alcohol concentration of more than 0.05 percent, these devices are meant to
detect whether a driver has more than a certain defined amount of THC in their
saliva. If so, then the test should come back positive. THC is the principal
psychoactive constituent of cannabis.




FALSE POSITIVES AND NEGATIVES

Study participants were occasional cannabis users who consumed two different
types of cannabis or placebo cannabis on three separate test days. Participants
had their saliva tested at baseline and at regular intervals after cannabis
consumption using the Securetec DrugWipe and the Draeger DrugTest 5000 – the
same types of devices that are in use around Australia for MDT.

The study tested 14 participants on two devices where the participants had
vaporised placebo cannabis, THC-dominant cannabis, or cannabis containing
equivalent concentrations of THC and the non-intoxicating cannabinoid CBD
(cannabidiol). The tests were conducted at four different timepoints. In all,
there were more than 300 separate tests taken. Participants were also tested for
driving performance on a state-of-the-art driving simulator.

As well as using the two MDT test devices, the researchers collected separate
saliva samples in order to measure exactly how much THC was in each
participant’s saliva at the time of each test. This “confirmatory” test used a
highly accurate laboratory mass spectrometer. 

“What we found was that these test results often came back positive when they
should have been negative, or conversely that they came back negative when they
should have actually been positive,” Mr Arkell said.

The study also found that measures of accuracy, specificity and sensitivity of
the two devices fell below the levels recommended by EU authorities.

The rationale for mobile drug testing is based on the success of the RBT program
pioneered in Australia. But while there is a very clear link between alcohol
intake, blood alcohol content measured in a breathalyser, and intoxication, THC
levels in saliva do not reliably reflect cannabis intake or intoxication.


NEW METHODS NEEDED

“We should instead be focusing on developing novel methods for detecting drivers
who are actually impaired by cannabis. The two devices used by police in MDT
were never designed to measure impairment. Authorities in other jurisdictions,
such as Canada, remain far more cautious in their use of such
devices,” Professor McGregor said.

Professor McGregor said that when people use THC capsules or suppositories,
neither of which leave traces of THC in the oral cavity, users have zero THC in
their saliva, but can be heavily intoxicated. Additionally, people tested in
this study would often feel too impaired to drive two hours after vaporising
cannabis but would give a negative saliva test with the two devices.

Conversely other people in the study presented with negligible levels of THC in
their saliva, and no driving impairment, but tested positive with the MDT
devices at the detection thresholds used in the study.

There is also the issue of passive smoking, Professor McGregor said, that at
least two overseas studies had shown that people passively exposed to the
cannabis smoke of others can exhibit salivary levels of THC that would generate
a positive test result.

The number of mobile drug tests being conducted each year continues to rise,
with NSW Police planning to conduct 200,000 of these tests in 2020.

Study lead Mr Arkell said: “Given that these tests can cost at least $40 each –
and potentially lead to serious life-changing penalties for drivers – it is
imperative that these concerns around reliability and accuracy are addressed.”


FUNDING DECLARATION

This study was supported by the Lambert Initiative for Cannabinoid Therapeutics,
a philanthropically funded centre for medicinal cannabis research at the
University of Sydney.


BACKGROUND INFORMATION

Use of roadside saliva tests in Canada for impairment in question

https://www.ctvnews.ca/autos/use-of-roadside-saliva-tests-for-cannabis-impairment-remain-in-question-1.4381731

Studies into passive smoking of cannabis
Cone et al (2015) DOI: 10.1093/jat/bkv070
Moore et al (2011) DOI: 10.1016/j.forsciint.2011.06.019




LAMBERT INITIATIVE

For Cannaboid Therapeutics



IAIN MCGREGOR

Professor, Psychopharmacology
Email
 * iain.mcgregor@sydney.edu.au





MARCUS STROM

Media Adviser
Phone
 * +61 2 8627 6433

Mobile
 * +61 423 982 485

Email
 * marcus.strom@sydney.edu.au





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