Two papers have appeared evaluating interferences in glucose meters. These studies are method comparisons with the added information of the medication(s) taken by the subjects. This paper contrasts a traditional interference study with the method comparison protocols. Unlike the advice in CLSI EP7, a substance that interferes should be reported even if the level of interference is clinically acceptable. The evidence of no clinically important interference in the method comparison protocol is very weak, and there is no possibility to detect statistically significant interferences. I provide an example where vitamin C at a therapeutic level was within clinical error limits, but when the concentration was at levels used to treat cancer, there was bias well above clinically acceptable limits.
Keywords: EP7; ISO 15197; glucose meter; interference.