On the Dexcom G6 system, the sensor is factory-calibrated according to a parameters and associated response in the sensor, and assigned a calibration code. There is still work being done, but it appears that dexcom is using the following sensor codes:
Since these codes are presumably based on certain parameters and associated sensor responses, it would not be a good idea to just randomly choose a code for a sensor if you were uncertain of the sensor’s assigned code. In other words, save the paper if you intend on restarting a session using a sensor code.
No-Code vs Code sessions
Sensor Code sessions: A sensor session that was begun using the assigned sensor code will not prompt for initial BG values at the end of the 2-hour warmup nor during the session. For the 10 days, you should not expect to have any prompts for finger checks. Having a sensor code entered should help the sensor maintain accuracy without the need for finger sticks and calibrations.
No Sensor Code sessions: A sensor session that was begun by choosing the “No code” option will ask for 2 initial calibration BGs after warmup. After that, the session will prompt the user for a calibration point 12 hours later. If that calibration is not given, the prompt will reappear until it is given. Inputting a calibration point resets that timer and you won’t be bothered for another 12-24 hours for a calibration.
Calibrations vs No Calibrations
Even with an active Sensor Code session (aka no-calibration prompts every 12 hours), there may be times when you should calibrate. Dexcom has a very helpful set of G6 calibration guidelines to help you decide if/when to calibrate. They are very useful for your 10-day old or less sensor:
- When meter BG is less than or equal to 70 mg/dl, calibrate if sensor BG is 30 mg/dl or more different from meter value.
- When meter BG is above 70 mg/dl, calibrate if sensor BG is not within 30% of the meter value.
- If a calibration does not bring the sensor into acceptable limits, repeat the process 15 minutes after the first calibration.
- If a series of 3 calibrations, each entered 15 minutes apart, does not bring the sensor back into acceptable limits, call Dexcom to discuss getting sensor replaced.
Using these guidelines, it was pretty easy to identify our recent bent wire sensor when it wouldn’t settle down early in our session.
Personal experience tells me those Dexcom rules are generally pretty good with a couple of additions:
- Don’t enter a calibration point during times of rapidly changing BGs. Try to find a smoother time of day where food and insulin bolusing is minimal and BGs are calm.
- Don’t let the new sensor just flail on a bad starting point. If the initial BGs starting a Sensor Code session are not within acceptable range of the meter readings, calibrate.
- Don’t calibrate when very high or very low.
- Don’t calibrate during compression lows.
If you get beyond 10-days and are having problems with the sensor maintaining accuracy, it’s best to just replace the sensor vs. suffering through jumpy, inaccurate BG data.
Q: Do I need to calibrate every time I am prompted in a No Sensor Code session?
A: Not necessarily. You should calibrate at times that make sense as opposed to simply calibrating on a schedule. For example, calibrating at 9:00 am just because a prompt showed up may not be the best idea if you just at a bowl of cereal at 8:30 am.
Q: What happens if I don’t calibrate when prompted?
A: If this is a normal, timed calibration prompt, nothing will happen. Your sensor session will keep going. You’ll get reminders until you finally do calibrate. If you don’t want to be pestered with those alerts, you can go into your phone’s Notification settings for the Dexcom G6 app and turn off banner notifications. Then you won’t be bothered by the little notification banners that appear.
Q: But what if I really never calibrate during a session?
A: The Dexcom G6 was approved for 10 days of no-calibration mode. After that, you are in the “what makes you comfortable?” realm. If you are restarting sensors, you will likely find that your sensor’s accuracy will decrease over time. Calibrating may help restore accuracy for awhile. However, you should never keep extending your sensor sessions to the point that the sensor is unable to maintain decent accuracy. If you are needing to consistently calibrate often to maintain accuracy…it’s time to replace the sensor IMO. Clinical trials were run with once-per-day calibrations. There are lots of people who go days without calibrating. Personally for us, we test (but don’t calibrate) every morning no matter what. If we find the sensor is starting to lose accuracy on those morning readings, we plan on replacing the sensor.
Q: How has your sensor accuracy been after restart?
A: Pretty darn good. We enter the sensor code during restarts and the sensor is maintaining its accuracy quite well. We use CGM data in our closed-loop system, so accuracy is quite important to us. We have not noticed any sudden or crazy drop-off in accuracy from a restart.
Q: How many restarts can you do on the G6?
We are finding, just like with our G5 experience, that we don’t get much extended time out of a restarted session before the sensor kind of “drifts” off its accuracy. My daughter usually never gets more than about 13-14 days per sensor before we find the accuracy decreases enough that we want to replace it (remember we loop with this so accuracy is important). I expect that your ability to maintain accurate sensor data with the G6 will be similar to whatever you got on the G5. If you went 20 days before on the G5, you’ll probably get similar from the G6.
Restarted Sessions with Reset Transmitters
My original blog post on G6 restarts indicated that all restarted sessions would end up behaving as No Code sessions (i.e., sending calibration prompts twice per day) regardless of whether or not you entered a sensor code during the restart process. After further testing and feedback from other users, I think I’ve narrowed down the source of the issue. I was using a reset transmitter for much of my testing. Subsequent testing has revealed a little more information:
Reset transmitters will cause EVERY session (new and restarted) to be a “No Code” behavior and you will get calibration requests…even if you entered a sensor code.
If you are using a normal transmitter that has not been reset, you should be able to restart sessions using the sensor code, and not have calibration prompts. If however, you are using a reset transmitter, you’ll get calibration prompts on every session, even brand new sensors. So if you intend on using your transmitter beyond 112 days or replace the battery, you can say good bye to no-calibration sessions.
How to enter code?
There have been reports of regular (non-reset) transmitters still yielding calibration requests even when the sensor code had been entered I believe that issue, according to what I’ve been told and read, is an issue with the app’s failure to properly read the sensor code when users use the camera feature to enter the sensor code. Therefore the current recommendation is to always manually type in your sensor code instead of using the phone’s camera.
I’ll be updating that blog post to reflect the new info shortly.