This work quantitatively extends former conclusions drawn for the mechanisms of enzymatic reactions in homogeneous solutions. It evidences that any straightforward use of data extracted from calibration curves performed for an electrochemical enzymatic sensor in usual homogeneous bulk solutions is delicate or even impossible whenever the sensor main purpose involves monitoring the same substrate under very different conditions, e.g., under in vivo or ex vivo situations. This is even more debatable whenever such enzymatic electrochemical sensors are used to record local transient emission of the enzyme substrate within living tissues, or near or inside single cells. Indeed, the coupling of enzymatic responses with diffusional transport of the substrate is radically changed as will be reported in a separate work.