The researchers analyzed all weekly patches but did not test every daily patch when its corresponding weekly patch was negative. The daily results should not be described as an exhaustive independently measured daily series.
The testing rule followed collection
In the oral-THC arm, daily and weekly patches were collected during washout, dosing and follow-up. The methods specify that some daily patches were not tested if no THC was found in the corresponding weekly patch. All weekly patches were tested.
This distinguishes a patch that was collected from a patch that actually supplied an analytical result. A missing daily analysis is not another measured negative.
The design supports a bounded conclusion
No analyzed daily or weekly patches contained quantifiable THC after the studied oral regimens. That observation does not establish analytical findings for every untested patch, nor does it prove that every possible oral dose is undetectable in sweat. The weekly result was used as a practical condition for some further testing.
What a forensic summary should retain
Report the tested specimens, wear intervals and quantification limit rather than inflating the number of independently observed negatives. The study documented route- and protocol-dependent detection, not a universal sensitivity estimate. Sweat results also do not determine a person’s functional state at a particular moment during a multiday wear period.
Related reading: cannabinoid assay validation.
Research cited
Huestis and colleagues (2007). Excretion of Δ9-Tetrahydrocannabinol in Sweat. DOI: 10.1016/j.forsciint.2007.04.002.
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