I’ve had the “Do not calibrate. Updating Sensor” message a few times. Each time the transmitter was bumped and the adhesive let go, causing the sensor probe to partially pull out. I’ve always had to replace the probe after this happens. After it completes it’s “update” It will give me a calibration not accepted error the next time I try to calibrate it.
Glucose sensors work by using an enzyme (like glucose oxidase) that produces hydrogen peroxide (H2O2) as it reacts with (breaksdown) glucose. The H2O2 diffuses through a special membrane that is permiable to H2O2 onto the working electrode,
The working electrode has a special catalyst coating (platinum?) material that contains binding sites where hydroxide ions (OH-) are bound to the metal atoms at the surface. The H2O2 can adsorb (stick to) these binding sites to form a complex. The complex will then undergo an internal electron transfer, and cause the H2O2 to break down, reducing (extra electron) the binding site, and releasing H20 and O2 as byproducts. As the binding sites return to their original state, they release hydrogen ions (H+) and cause a tiny current to flow in the sensor electrode.
The current is what the sensor measures, and uses to determine the blood glucose concentration.
The “Updating Sensor” messages occur whenever there is a rapid shift in sensor current. This can happen if the sensor becomes dislodged, as the total sensor current depends on the contact between the sensor and the interstitial fluid. Less fluid contact means a proportionally smaller sensor signal.
The “updating sensor” error is the 670G basically saying “Whoa! What happened? I suddenly lost half my sensor signal!”
Like I said, I haven’t had any luck fiddling around with trying to calibrate after an “Update Sensor” message. If you want my advice, just save yourself 3 hours, and change the sensor, because you’ll more than likely be replacing it anyway, when the 670G will not accept calibrations on the “updated” sensor.