Finger prick test detects THC levels at roadside traffic stops

This research presents a breakthrough method for detecting cannabinoids in just 50 microliters of blood—roughly the size of a drop from a finger prick. Using advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS), researchers developed a highly sensitive test that can measure THC, CBD, CBN, and other cannabinoids at sub-nanogram per milliliter levels. The method addresses critical limitations of existing dried blood spot tests, which can be inaccurate due to hematocrit variations, and volumetric microsampling devices, which are expensive. By using liquid-liquid extraction with sodium hydroxide alkalinization, the team achieved detection limits as low as 0.10 ng/mL for THC—more sensitive than most methods requiring larger blood samples.

The most significant application is roadside cannabis impairment testing. Current approaches require trained phlebotomists to draw larger blood samples at medical facilities, causing delays during which THC levels naturally decrease in the bloodstream. This new method could enable police to collect a simple finger prick sample at the roadside, capturing THC levels at the actual time of driving rather than hours later. The technique overcomes three major barriers: the need for large sample volumes, dependence on medical professionals for blood draws, and the problematic delay between traffic stops and testing.

This validation study demonstrates that microsampling approaches can match or exceed the sensitivity of traditional laboratory methods while being far more practical for field use. The research team achieved linear calibration ranges up to 300 ng/mL for all cannabinoids tested, making it suitable for both medical monitoring and forensic applications. While primarily developed for impaired driving enforcement, this ultra-low-volume testing method could also benefit cannabis research, therapeutic drug monitoring, and situations where obtaining large blood samples is challenging.