Pooled Drug Challenges Defined the Saliva Assay’s Interference Evidence
The saliva assay tested five pools of ten drugs for interference. Its favorable result supports those tested challenges, not an assertion that no possible drug or metabolite can affect the method.
What the challenge measured
Drug pools were added to blank oral fluid fortified at the low quality-control level. The reported cannabinoid biases ranged from approximately −17.4% to 12.7%, within the acceptance framework used for the experiment. The investigators therefore found no unacceptable quantitative interference from the tested pools.
The drug list and concentration matter
A selectivity experiment is bounded by the substances, concentrations, combinations and analytical conditions examined. Another compound, concentration or specimen characteristic is not automatically covered. A pooled challenge can be useful without representing every exposure that might occur in an unknown forensic specimen.
Apply the result without exaggeration
A claim that a particular medication interfered needs evidence relevant to that medication and assay. Conversely, the phrase “validated LC–MS/MS” is not a complete answer to a specific untested interference concern. Review the challenge list, acceptance criteria and chromatographic data together. The study evaluated an oral-fluid measurement method, not a universal test of whether a person was impaired or how much cannabis was taken.
Related analysis: the oral-fluid assay’s small human illustration.
Research cited
Sobolesky and colleagues (2019). Validation of a liquid chromatography-tandem mass spectrometry method for analyzing cannabinoids in oral fluid. DOI: 10.1016/j.cca.2019.01.002.
