Short-Lived Blood Cannabinoid Markers Were Not Detected in Every Recent Smoker
A marker can have a short detection window yet still miss people who used cannabis very recently. A controlled-smoking study demonstrated incomplete detection of several proposed minor-cannabinoid markers even near their observed peaks.
Paired whole blood and plasma
Ten participants smoked one cannabis cigarette containing 6.8% THC on a closed research unit. Investigators directly measured free and glucuronidated cannabinoids in whole blood and plasma, with prompt analysis intended to minimize storage changes.
The paired matrices were not interchangeable. Concentrations and detection rates differed, so an analytical result or cutoff in plasma could not simply be assigned to whole blood.
Short detection did not mean complete sensitivity
Near the observed peaks, CBD was quantifiable in 60% of whole-blood samples and CBN in 80%; THC-glucuronide was detected in 50%. Corresponding plasma detection rates were higher.
CBD and CBN were not detectable after one hour under the method and product conditions. Those short windows motivated interest in recent-use identification, but incomplete peak detection means that a negative marker cannot exclude recent smoking.
The product and assay define the boundary
This was a small, predominantly male sample using a particular cannabis cigarette. Modern products with different minor-cannabinoid content may produce different profiles. The assay’s quantification limits also helped determine the observed windows.
Samples were processed rapidly and analyzed within 24 hours, conditions that may differ from routine casework. The results support further study of combined markers, while leaving an individual impairment threshold unestablished. Recent exposure, detectable minor compounds and reduced functional ability are related questions that require different evidence.
Related: Interpreting cannabinoid measurements.
Primary research
Identification of Recent Cannabis Use: Whole-Blood and Plasma Free and Glucuronidated Cannabinoid Pharmacokinetics following Controlled Smoked Cannabis Administration. Clinical chemistry (2011).
