Calibration question

Last night I did a calibration, as demanded by Dex. The Dex said I was 120, and my glucometer said I was 121... but when I entered the 121, Dex came back with a 129! I know its not a horrible difference but should it be higher than the two other values?

BTW, I'm on day 20 with this sensor and it is coming off tomorrow... there's just no sticking the tape on anymore.

I have experienced this as well. My only explanation is that the Dex is measuring trends and it was probably an indication that your BS was slowly increasing. I have checked again in about 15 minutes and found the Dex to very close. It lags by about 10-15 min.
Hope this helps.

I have also experienced this and found it to be close to the finger stick take again in about 15 minutes or so. Remember the dex is looking at your trending data. Numbers are great but the trend lines are what I focus on myself.

This is normal and consistent with the algorithmic calculation done by Dexcom. Keep in mind the way Dex works.

It works by looking at the current generated by the chemicals on the sensor wire. The transmitter looks at the current and transmits the current value to the receiver. The receiver calculates where the current value compares to your BG and then displays a statistically accurate value based on all the technical gobbledy gook.

What was the last reading on the Dex prior to its asking you to calibrate? If it was down near 100, then it makes no sense that you got the 129, however if it was up in the 130s or 140s, then the 129 makes perfect sense.

And then everything that Jay said. :)


Keep in mind most finger sticks are ± 10% of true while most CGMs are ±20% but show trends very well.

All things equal. Keep good notes for a while noting the arrow directions and how many. For example up at 45 degrees vs two up at 90 degress. Learn the exact mg/dL each means. After you have several days, call Dexcom tech support and ask them to explain all of the variations to you. I had to listen several times to learn this.