A cannabinoid measurement depends in part on how the laboratory prepares the sample. Pigliasco and colleagues paired volumetric absorptive blood microsampling with liquid chromatography–tandem mass spectrometry. Their assay measured CBD, THC and several metabolites, including 11-hydroxy-THC and THC-COOH.
The method used overnight enzymatic glucuronide hydrolysis before extraction. This step can release analytes from their glucuronide conjugates. A method that includes hydrolysis can therefore report a different quantity from an assay designed to measure only the unconjugated form. The extent of that difference depends on the specific analyte and method.
The investigators applied their method to blood from seven patients who received CBD-containing formulations. That application illustrates use of the assay in the sampled setting. Before comparing its results with another report, check whether the methods used the same specimen type, targeted the same compounds and handled conjugates in the same way.