Freezing Was Not Always Better for Preserving Saliva Cannabinoids
A colder storage temperature did not always preserve saliva cannabinoids better. In authentic specimens, the effect of freezing depended on the collection device and the compound being measured.
The study compared two collection systems
Sixteen participants smoked a cannabis cigarette, and researchers collected oral fluid with StatSure and Oral-Eze devices. Samples from different times were combined into a separate pool for each participant and device, providing enough material to compare storage conditions.
Baseline concentrations were measured within twenty-four hours. The study classified concentrations within 80–120% of baseline as stable. Refrigerated conditions included one and four weeks at 4°C; frozen conditions included four and approximately twenty-four weeks at −20°C.
The device changed the freezing result
For StatSure pools, all sixteen participants’ THC results remained within the stability range under the tested conditions, including the longest frozen interval. For Oral-Eze pools, all sixteen THC results met the criterion after four weeks refrigerated, but only thirteen did after twenty-four weeks frozen.
The pattern was analyte-specific. Only five of nine evaluable Oral-Eze CBD pools met the criterion at the longest frozen interval. That is a proportion of stable specimens, not a claim that every CBD specimen retained exactly 56% of its starting concentration.
A collection buffer is part of the specimen
Device buffers and dilution ratios differed. Cannabinoids below quantification at baseline could not supply an informative percentage-retention comparison, reducing the evaluable counts for some analytes. Pooled post-smoking material also does not represent every individual collection time or low-concentration case specimen.
The data do not justify a universal instruction to refrigerate every saliva sample or an exact correction for a stored result. They show why laboratory validation must cover the actual device, analyte, temperature and duration. A general assumption that freezing can only improve stability is inadequate, and preservation of a concentration remains separate from interpretation of impairment when the sample was collected.
Related: interpreting THC concentrations separately from impairment.
Primary research
Impact of Oral Fluid Collection Device on Cannabinoid Stability Following Smoked Cannabis. DOI: 10.1002/dta.1688.
