Dried Saliva Cannabis Identification Was Validated Qualitatively
A dried saliva spot can support identification of THC or CBD without supporting an exact concentration. An extraction study validated a qualitative LC-MS/MS method and explicitly left quantitative validation unresolved.
The validation used fortified specimens
Researchers prepared dried oral-fluid spots using pooled drug-free saliva. In the validation procedure, oral fluid was first dried on filter paper and cannabinoid standard was added afterward. That preparation is not identical to collecting saliva from someone who has used cannabis and drying the complete specimen.
The study assessed identification, interference, carryover, matrix effects, recovery, detection limits and storage. Eight blinded simulated specimens were correctly classified for THC and CBD. Authentic post-use specimens were not available for that application exercise.
Low recovery limited the method’s scope
Extraction recovered approximately one-quarter of the cannabinoids. The established detection limits were 2 ng/mL for THC and 4 ng/mL for CBD. Sensitive instrumentation enabled detection despite the losses, but the authors reported that recovery problems impaired quantitative method validation.
This separates two legitimate questions: whether the compound can be identified, and whether a numerical result accurately represents the original specimen. Correct classification of eight simulated specimens does not establish concentration accuracy across clinical or forensic populations.
The higher-recovery alternative tested a different workflow
Weak-anion-exchange-and-salt pipette tips recovered approximately 91% of the cannabinoids in an exploratory comparison. That experiment used freshly fortified liquid oral fluid extracted immediately, at one tested concentration. It did not establish that the same recovery would occur after routine collection, transport and storage or validate a complete quantitative casework method.
Dried specimens retained approximately 70% of the tested signal after 35 days at 6°C. That observed loss should not be described as perfect preservation. Collection format, fortification sequence, extraction and storage belong in the interpretation. None of these analytical results establishes an individual impairment threshold or a validated saliva-to-blood conversion.
Related: interpreting THC concentrations separately from impairment.
Primary research
Study of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) extraction FROM dried oral fluid spots (DOFS) and LC–MS/MS detection. DOI: 10.1186/s42238-021-00088-8.
