Reading the Reported Dilution Results in a Cannabinoid Saliva Assay
The saliva assay tested dilution of high-concentration samples, but its reported results should not be reduced to a blanket statement that every dilution met the stated acceptance criterion.
High samples were diluted into a defined matrix
The method-development study evaluated 1:2, 1:50 and 1:200 dilutions using blank oral-fluid–buffer mixtures. This challenged whether samples above the ordinary calibration range could be prepared for measurement through a specified procedure.
The investigators stated a dilution-integrity criterion of results within 20% of the target. In the results, reported accuracy ranged from 85.1% to 97.8% of target for Quantisal preparations and from 77.1% to 105.8% for Oral-Eze preparations, with three replicates for each dilution factor.
The lower reported value deserves qualification
A value of 77.1% of target is below the 80% lower boundary implied by that criterion. The reported overall range does not identify, in that sentence, which individual analyte and dilution produced the lowest value. Assigning it to a particular cannabinoid without the underlying results would add unsupported precision.
The narrow conclusion is that the study investigated large dilutions and reported a range that includes a result outside its stated criterion. That is more informative than treating the entire exercise as either uniformly successful or wholly unusable.
Applying this to a high cannabis-test result
A high specimen concentration calls for the actual dilution factor, matrix, corrected calculation and laboratory acceptance decision. The validation concerns quantification of cannabinoids in oral fluid; it supplies no impairment threshold and no universal authorization to dilute any specimen by any factor.
Related analysis: collection buffers and cannabinoid quantification.
Research cited
Concheiro, Lee, Lendoiro and Huestis (2013), Simultaneous Quantification of THC, THCCOOH, CBD and CBN in Oral Fluid by MicroFlow LC–High Resolution Mass Spectrometry. DOI: 10.1016/j.chroma.2013.04.071.
