Virginia Forensic Scientists Validate Expanded Blood Testing for THC and Cannabinoids
Researchers at the Virginia Department of Forensic Science have developed and validated a more selective method for detecting cannabinoids in blood, supporting forensic investigations involving drug-impaired driving, death investigations and other criminal cases.
The work was conducted under the National Institute of Justice’s 2020 grant, “Expanded Quantitative Cannabinoid Testing in Biological Specimens to Combat the Ever Changing Cannabis Landscape.” The Commonwealth of Virginia received $290,353 for the project, which is now listed by NIJ as closed.
The Virginia DFS validation packet, dated July 27, 2023, documents a supported liquid extraction method followed by liquid chromatography-tandem mass spectrometry, or LC-MS/MS. The procedure uses two analytical columns to improve compound separation and confirmation, an important feature as cannabis products increasingly contain THC isomers and other cannabinoids.
The validated work focused on Δ9-THC, Δ8-THC, 11-hydroxy-THC, carboxy-THC—the principal metabolite commonly known as THC-COOH—and cannabidiol, or CBD. Testing was evaluated in blank blood, antemortem blood and postmortem blood. Urine was also examined, but the report states that urine findings were intended for qualitative analysis rather than quantitative reporting.
According to the report, the blood matrices met the laboratory’s predefined bias and precision criteria for the principal quantitative targets, including Δ9-THC, 11-hydroxy-THC and carboxy-THC. The validation also examined sensitivity, calibration, carryover, potential interferences, dilution integrity, stability and robustness across two LC-MS/MS instrument models. The work followed ANSI/ASB Standard 036, which sets practices for validating forensic toxicology methods.
The results also illustrate why expanded cannabinoid testing requires caution. The report identified an interfering signal associated with the Δ8-THC qualifier transition in some supported-liquid-extraction cartridges. Based on the validation data, Δ8-THC, CBD and cannabinoids tested in urine were recommended for qualitative use only. The report also noted matrix effects, including ionization suppression, that can affect instrument response and require careful method control.
NIJ describes the broader project as part of Virginia DFS’s effort to expand cannabinoid testing through automated sample preparation and LC-MS/MS. Unlike gas chromatography methods that may require derivatization, LC-MS/MS can analyze cannabinoids through a direct approach that simplifies preparation and helps preserve the compounds being measured. The agency maintains a toxicology research repository containing grant-related materials and method-development documents.
More capable laboratory testing can help investigators establish which cannabinoids or metabolites are present in a biological specimen. It does not, however, create a definitive blood threshold for cannabis impairment. Research summarized by the National Highway Traffic Safety Administration indicates that blood THC concentration does not have the same direct relationship to impairment as blood alcohol concentration. THC levels can fall rapidly after inhalation, while impairment may persist, and low concentrations may also remain in frequent users after impairment has ended.
The Virginia project therefore represents an advance in identification and measurement—not a standalone test for whether a person was impaired at a particular moment. Its value lies in giving forensic laboratories a better-validated way to distinguish Δ9-THC from related compounds, detect metabolites and document the analytical limits that courts and investigators must consider when interpreting cannabinoid results.
