Problems With Laboratory Only Determination of Impairment
WIS has highlighted key points in this article.
By Esther Carenza THE LAWYER'S DAILY
(Mar. 28 / 2019)
The institutions responsible for toxicological analysis of biological samples are imperative for the fair trial of cases involving allegations of driving while impaired by drugs. However, while they can be conclusive on whether a drug was detected, they will not have the ability to determine the timelines of a person’s drug impairment.
The Centre of Forensic Sciences (CFS) is one of the most extensive forensic science facilities in North America, comparable to the FBI centre in Quantico, Va., in matters where there is injury or death for crimes against persons or property.
The role of toxicology laboratories within the CFS or the RCMP will be to both analyze samples from cases involving allegations of impairment but also to provide interpretation of the analytical results and the other observations in the case in terms of supporting or refuting those allegations.
In the forensic toxicology laboratory, scientists can accurately measure the concentration of cannabinoids and other drugs and their metabolites in bodily fluids. However, accurate measurements of concentration do not of themselves conclusively imply impairment.
The implications of a given concentration measurement with respect to impairment differ widely between sample types (e.g., blood vs. urine) and between individuals. After a drug has entered into the bloodstream, the drug is distributed to the various tissues in the body and metabolism (chemical conversion of the drug to a metabolite, often predominantly in the liver) and elimination (including excretion into the urine via the kidneys) begins.
Drug and metabolite concentrations follow a complex trajectory, with considerable variability between individuals. Blood drug concentrations decline from the maximum value reached after a given dose in a non-linear manner (unlike alcohol, where the blood alcohol concentration declines by a constant amount per hour), precluding the ability to accurately predict a blood drug concentration some time prior to sample selection.
Since psychoactive drugs affect performance through actions on the brain, the best biological sample at the police’s disposal to act as a surrogate indicator of drug effects in respect of the impairment sections in the Criminal Code of Canada is blood. Section 9(A) of the Police and Criminal Evidence Act 1984 allows for an intimate sample, blood to be drawn from a person “only by — (a) a registered medical practitioner; or (b) registered health care professional.”
This requirement must necessarily lead to substantial delays between the issuance of the demand and the time of blood drawn for those jurisdictions without such personnel on site or on call.
In light of the new legislation regarding legalized cannabis use, Canadian police forces may elect to use certified phlebotomists, as opposed to hospital or clinic personnel, to draw blood in suchcases. Any delay in sample collection, can limit the interpretive value of the blood analysis result, since the concentrations of some drugs decline extremely quickly after last use. This is true in cases of cannabis or cocaine use, and may result in measured drug or metabolite concentrations that make recent exposure difficult or impossible to discern.
The Criminal Code of Canada also provides for the collection of alternative samples (oral fluid or urine) following the completion of assessment of a Drug Recognition Expert (DRE) officer. When looking at all the biological samples, blood is typically the gold standard in relation to urine. Oral fluid is more informative than urine as an indicator of which drugs are actively circulating in the blood. Oral fluid is inferior to blood in this capacity because oral fluid is not in direct contact with the brain.
Drugs arise in oral fluid either through partition from drug-positive blood, or through contact of the oral cavity with the drug prior to uptake into the blood (as would occur when cannabis is smoked, “vaped” or eaten. Numerous processes influence the relationship between drug concentration in oral fluid and corresponding drug concentration in blood, including the chemical properties of the drug and the extent to which the drug is bound to proteins in the blood.
For decades, scientists such as Marilyn Huestis have studied how the chemicals in cannabis affect the bodily systems (i.e., drug effects), and are processed by the body (i.e., time course of their effects and how long they are detectable, including those chemicals that are formed by the metabolism of cannabis constituents).
Cannabinoids may be defined as chemicals that act on the cannabinoid receptors that exist within the body. Three cannabinoids that are of primary interest currently are delta-9-tetrahydrocannibol (THC), the primary psychoactive chemical in cannabis, its psychoactive metabolite 11-hydroxyTHC, and cannabidiol (CBD), a non-psychoactive chemical that has shown therapeutic potential.
There are more than 500 compounds in cannabis which have not been studied and may singly or coupled with others contribute to impairment. Prohibition of cannabis products and their use for recreational purposes, as well as the cultural trend towards fear of those products as inherently dangerous, has slowed objective research into their therapeutic potential (or lack thereof). The same applies to research into the effects of high potency cannabis and ingestion of cannabisinfused food products on task performance and the concentrations of various cannabinoids in different body fluids. More data is required to better clarify the spectrum of effects across different users, different formulations and different exposure patterns.
Canadian law uses the word “impairment” in a binary sense; one is either impaired by a substance or is not, with respect to performance of a specific task or tasks. In reality, the impairing effects of any given drug on a task such as driving must be considered to lie on a continuum.
The magnitude of impairment is particular to dose, how the drug was taken, the user’s past experience with the drug (i.e. drug tolerance) and the nature of the specific task (implying that someone can appear to be completely sober to an observer, but specific task performance, including driving, may still be impaired in comparison to that of the same individual in a drug-free state).
With cannabis, and unlike alcohol, the correlation between blood THC and 11-hydroxy-THC concentrations and the degree of impairment is poor. Thus, it is critical to establish whether recent use occurred in conjunction with observations of the officers involved with the traffic stop and any psychomotor or physiological tests.