New Dexcom wearer

My son is on day 3 of wearing the Dexcom with Share and we LOVE it so far. I have a couple of questions though:

1) I've read that you can sometimes get 2 or even 3 weeks wear out of one sensor. How does one restart the same sensor. Do you end the current sensor session and then restart a new one without replacing it?

2) Sometimes when we add in a blood sugar, the CGM changes but not to the blood sugar we added. For example, my son was 138. The sensor said he was 132. He added in 138 but it jumped to 140. It's not a big difference but it seems odd that it did not jump to the blood glucose that we added.


1) I am starting my 3rd week now. I hit the "Stop Sensor" menu item. I wait for a couple of seconds and then "Start Sensor". About 2 hours later it comes on with the 2 drops of blood for you to enter the calibrations. Then I go for another week.

You will know when it is time to replace the sensor when you see ??? for an hour or so at a time and the meter is way off from your tests.

I have gotten a max of 5 weeks and a day, once or twice, but I average about 3.5 weeks, for the past two years and two meters.

2) Since it is knowing what your BG is doing, i.e., going up, down or all around, the Dexcom uses a logarithm it has been programmed with to estimate the current. It can go up some, down some or not change at all. Also, consider the information it has is from about 5 minutes ago and you are entering current readings so it adjusts for that also. This is what the rep told me at one of our Monthly Type 1 group meetings a few months ago.

I hope that helps.

Perfect- thank you!

I usually wait until the sensor stops after one week, and then restart it. You get warnings for a few hours that the sensor is almost done. You might decide to stop it and start it again earlier, for instance if the two hour startup time will be inconvenient for you.

I Stop Sensor, wait a few seconds and then Start Sensor. Very easy!

I wear mine for two weeks, tops. Starts to wig out on me after that.

Yeah, it's funky that you say - hey Dex, I'm 105 and Dex says 98. It's still in the good zone!

Best of luck! Dex changed my life.

My daughter is also on day 3 of wearing her first sensory and we have had similar occurrences. I figured it was a learning curve and will eventually even out, though we still keep records of her blood glucose levels when she uses her glucometer. I also read via other posts that people have worn their sensory's for 2-3 weeks too, and would benefit by knowing how to calibrate the sensor that my daughter is currently wearing too. I feel more relieved knowing that I am not the only parent whose child (my daughter just turned 24! but is having tremendous emotional issues in dealing with her newly diagnosed LADA) just started using the Dexcom.

You just keep calibrating as you normally do and then when it is time to stop sensor - stop the sensor, wait a few seconds and start sensor. I rarely have on the money BG's on my Dex and my meter. But it is within the percentage that Dexcom says is acceptable. You can't have it say the same thing as the meter 100% of the time. But, if you are unsure, you should always do a fingerstick.

I did wear one for about 3 weeks. Just go to the menu - stop sensor - and then restart sensor.I think I have an allergy to the adhesive. The last sensor I just pulled out because it was very inaccurate. It was reading 90 while my blood sugar was 140. And I was itchy from the adhesive...Have bought a couple of adhesive barrier products to try to prevent this from happening and am hoping it will help everything to stay on better.

Looks like your numbers were right in line with your meter readings. They sometimes are exact, but mostly within a few points of each other. There is also a lag time between the reading from the Dexcom versus your meter of about 15 minutes.

Welcome to the "Dexcom family" -- I personally love mine - going on two years soon... I use sensors for an average of 2.5 weeks, though I've had many last well into 3 weeks and one go longer yet.

The biggest issue, is keeping it stuck as long as I'd like - for that, I add tape - I use Opsite Flexfix tape and repair it as needed. I change when I see ??? too much, get crazy readings, or it loses the signal several times. Aside from more reliable readings often during week 2 and 3, I also find that I just get more comfortable with the location of the sensor and forget it's even there, when it's been there for longer.

As to the number it displays after a calibration, it has to do with the algorithm they use, which takes a combination of the numbers you enter and the readings it gets from interstitial fluids. Meters are not perfectly accurate, either, after all. One support tech advised me that, when it's seems too far off, it might be possible to really re-calibrate it by entering 3 fingerstick readings 10-15 minutes apart. That is supposed to make it favor the entered numbers over its calculations.

Good luck!

Thanks for the help everyone. As a follow up - is it common to see such big differences in the CGM when running low? My son had a 57 today but his glucometer (Omnipod PDM) said he was 87. A reading of 57 prompts me to intervene in a much faster/bigger way than an 87 :-) I think the PDM was wrong as he did not 'feel' like he was 57 and he had added a blood sugar reading to the CGM just a hour earlier.


One more point about extending your sensor beyond 7 days. You will need to use additional adhesive/tape to stick it down otherwise it will start to peel off. I use a combination of Opsite Flexfix tape and Skin Tac adhesive. If you hunt through the posts on the Dexcom group you will find loads of posts with details of how best to do this.

If you truly believe that the error was in the BG meter, then you want to check to see if it is in fact working correctly and replace it if it is not, no?

You already pointed out in your post why that would be a priority. A reading of 57 is more concerning. And while meters are not expected to be 100% accurate, they should not be "off" by that much especially for values which are in the so-called "normal" range of 70-120 (?) or so.

Of course, it is possible that the meter result was wrong because of some contamination to the sample. Did your son wash his hands before testing?


I was told by a support tech that it looks not only at the last entered calibration reading but also at the 1 before, & it allows for the interstitial fluid lag. That would explain why Thas' advice of 3 readings to favor the entered number.

For the new users of the Dex CGM, I can offer a few tips. The Dexcom algorithm sometimes acts strangely when you add a calibration number. It is trying to negotiate the sensor trending numbers and the lag time between the sensor number and the fingerstick capillary number.

I’ve experienced episodes where the Dex might be reading 60 and fingersticks are reporting 80. Then I’ll calibrate 80 and the CGM will insist 60 or less! I’ll fingerstick 15 minutes later at 80, enter the calibration and still have Dex insist 60. I don’t get that either.

I don’t like that since time less than 65 is a number I follow for management purposes. I’ve adopted the habit of always washing and drying my hands before a calibration. I also do two fingersticks and average them for the calibration number.

I never calibrate when the display shows angled or up/down arrows, only when they’re pointing sideways. I try to only calibrate twice per day when the Dex asks for it. I will add calibrations when the two fingerstick average is off by 30 points or more and the arrow is sideways. I’ve witnessed many times when I was tempted to calibrate and did not but then the Dex adjusted and trended toward my fingerstick reading.

Patience and an easy hand on the helm are often rewarded with Dex accuracy.