Oral Fluid Testing: Roadside vs. Evidential Analyses

Posted on September 02, 2025 in Uncategorized

Written by Ashley M. Hart

As cannabis is being decriminalized in many states, there has been increased interest in rapid roadside tests to detect THC and other substances for intoxicated driving charges. A majority of states now have oral fluid testing in some form: roadside (presumptive) or evidential (confirmed in a lab). These states include Alabama, Alaska, Arkansas, Arizona, California, Connecticut, Georgia, Illinois, Indiana, Kansas, Kentucky, Maryland, Minnesota, Mississippi, Missouri, Montana, New York, Nevada, North Dakota, Ohio, Pennsylvania, South Dakota, Tennessee, Utah, Virginia, Wisconsin, and Wyoming.

Michigan has pending legislation that would make a roadside saliva test a presumptive test that an officer could use to support an arrest decision, but the roadside saliva result would not be admissible at trial except under certain exceptions.

Funding and implementation have come through a few different avenues: legislation with funding from state legislature (Minnesota); funding from state highway safety offices and implementation by law enforcement (Arizona, Indiana); funding from and implementation by law enforcement agencies (California, Illinois, Montana); or funding from state agency like a forensic lab, coordinating with law enforcement and others for implementation (Alabama). In some instances, pilot programs were completed before full implementation while in other instances, agencies barreled ahead with testing.

Police allege that the roadside test serves as an investigative tool to support probable cause. An oral swab is administered, placed into a buffer solution, and placed into a handheld machine to be screened.  The result is qualitative, not quantitative, either “positive” or “negative.” These tests are usually limited in scope to a small panel of classes of drugs. These results are not specific to the type of drug or its concentration, and they are not to be used in court proceedings. Moreover, they cannot be used to indicate impairment.

The other type of sample collected roadside is often referred to as an evidential oral swab. This is administered in a similar manner to the roadside test, with particular instructions on what part of the mouth to swab, and the swab is placed in a buffer solution and capped. These samples to be sealed and sent to a laboratory for further qualitative and quantitative analysis. A useful overview, including key critiques of a lack of manufacturing standards and inaccurate results can be found in this article: “Oral Fluid Drug Tests: Concerns and Recommendations”, published in the University of Michigan Ford School of Public Policy Science, Technology, and Public Policy periodical linked here https://stpp.fordschool.umich.edu/sites/stpp/files/2024-12/stpp-oral-fluid-drug-testing.pdf

While the lab results from evidential oral swab testing are more robust than roadside results and can be used in court, it is imperative to consult with a toxicologist and obtain your lab’s standard operating procedures in a complete discovery package to challenge these results. Challenges can be made from collection, preservation, and chain of custody to accuracy of results, the effect of methods of consumption on results, factors affecting the presence of a substance in one bodily fluid while being absent in another, and whether the results even indicate impairment.

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