The GC–MS/MS hair assay used a single-point calibration with separate controls and validated limits. It should not be described either as a full multi-point calibration in every run or as a method with no performance checks.
What the analytical protocol specified
Quantification used analyte-to-internal-standard area ratios, calibrated at 5 pg/mg for THC and 0.5 pg/mg for THC-COOH. The method also included drug-free controls, fortified controls and a blind quality-control specimen with each batch.
Reported quantification limits were 1 pg/mg and 0.1 pg/mg, respectively. The validated upper ranges differed between analytes. Calibration level, reporting limit and upper range were separate method characteristics.
Controls and calibration answer related questions
A control challenges whether a known material is reported acceptably; calibration supplies the response-concentration relationship used for calculation. One cannot silently substitute for the other. Assessing this design requires its validation and run-acceptance evidence rather than inferring accuracy from the number of calibrators alone.
Keep comparisons method-specific
The study also used an immunoassay with a different response and cutoff, which should not be merged with mass-spectrometric calibration. A result near a reporting boundary needs the actual method and units attached. None of these laboratory acceptance criteria independently establishes consumption quantity, timing or functional impairment.
Related reading: interpreting cannabinoid assay validation.
Research cited
Huestis and colleagues (2006). Cannabinoid Concentrations in Hair from Documented Cannabis Users. DOI: 10.1016/j.forsciint.2006.08.005.
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