First nite, and question about calibration

OK we went ahead and viewed the tutorials being as a Dexcom rep could not make it out to train us in a reasonable amount of time and we are anxious to start!

My son is 12 and also has mild autism . . . he was worried that the insertion of the sensor would hurt, but he didn't even flinch.

The first sensor did die on us within 30 minutes . . . I called Dexcom and they told me to remove it and asked if the wire was still intact on it; it was, so they said it probably wasn't anything we'd done wrong and they are sending a replacement.

Sensor #2 seems to be working fine so far, knock on wood, we're just four hours into it actually. The readings it is giving us are just 5 or so away from our Omnipod readings.

So my question to you old-timers is, the instructions say to calibrate once every 12 hours (or sooner if you want to). So how often should we calibrate? Does more information equal tighter numbers, or does it overwhelm the Dexcom?

Thanks for your advice.


I’m not an old-timer and will be anxious to hear what everyone else says, but my trainer told me to calibrate these 3 times:
-when you wake
-before bed
-anytime the dex reading is 50 points different from your meter.

I’m not an old-timer but I don’t think that calibrating more often will make much difference. With 38 days of data my Dexcom and meter values have averaged a bit over 8% difference. Feel free to try out the software I just created that will help analyze the accuracy. Sometimes the meter reads higher, sometimes the Dexcom reads higher. I think if you do several meter tests in a row you’ll find variation there as well. Both system will have variation. Despite the strict warning about not making treatment changes without using a meter I have absolutely no problem doing that based on the data I’ve seen so far. Even with a 20% variation it’s not going to hurt you to treat a low that’s not really that low or take some extra insulin for a high that’s not as high as it appears. I’m likely a bit unusual in this regard; I’ve been known to wake up low in the middle of the night and take some humalog before treating the low knowing full well that I’m going to overdo the treatment as I often do.

Well, I guess I am an old timer because I started with the DexCom Seven when you still had to calibrate using a LifeScan Ultra and a cable. I currently use the newer Seven Plus.

Usually I have found calibrating more frequently than every 12 hours actually creates less accurate results. This was confirmed by DexCom tech support. I initially found this out with the older unit because I checked my BGs with my meter 6-8 times daily. When the only way you could calibrate was to connect the cable to your meter, it transferred all the readings and my DexCom was usually way off. It was extremely frustrating. I eventually purchased a separate meter just to use for calibrations and the problem was resolved. It’s easier now because you can key in your readings and any extras don’t skew the results.

My rule of thumb is to calibrate according to the 12 hour rule. I always check my DexCom and compare it to my meter when I do a finger stick. If the reading is significantly different (> 50 points), I will add this as an extra calibration. It doesn’t happen often.

I calibrate whenever I know I have a good blood sugar, meaning that my hands are clean, no interference from lotion, soap etc or food, you can’t do too many calibrations, better to do them than to forget and have to wake up in the middle of the night. If you have ??? on the receiver, do not calibrate until they go away but the every 12 hours is the minimum after the initial 2 finger sticks so go ahead and calibrate. If you get a really out of whack blood sugar that seems really abnormal, not due to exercise, too much food etc. do not use that reading.

I only had the dexcom since Sept 9th. But I calibrate when I normally test (about 4 times a day min not counting when I think I am high or low). Since I already did the test I just enter it into the dex, and usually its on track. A few times its lagging, but hey cgms can lag a bit on occasions specially when rapidly changing glucose. I like to calibrate before I go to bed so I know it wont wake me in the middle of the night just for a calibration as it asks you every 12 hours and if I calibrate at 11 pm it wont ask me again until 11 am long after I am up. DO NOT calibrate with the ??? or the transmitter lost signal. Wait for them to go away. If the ??? doesnt go away within 3 hours call dexcom.

I usually calibrate when I test for meals and bedtime (4 times a day). Sometimes I forget and don’t calibrate, especially at meal time and if I am on the low side. I just want to get food into me so I can stop the downward trend.

That said, I have seen many posts which say to calibrate only when prompted, that too many readings “confuse” the CGM system. I have also read many times not to calibrate when bg levels are changing rapidly. Unfortunately that happens to me often, and if my meter reading is off by alot (I have been off more than 100 mgdl) I panic and calibrate to try to get the CGMS closer to what my meter says. One of my goals is to try to calibrate less and see if that helps.

My dexcom rep said that it does not matter if you do it every time you test or every 12hrs… Sometimes I wait for it to prompt me… Sometimes, I don’t (like if I’m going to be in the middle of teaching a class when I need to). I haven’t noticed any difference in how frequently I input the numbers. I have been on for almost 2months (and love it!!!).

New user, only on second sensor. I spoke with my Dex rep, she suggested day one to calibrate 3 to 4 times during the first day, and she thought it was better for the Dex to try to calibrate with lows and highs as it would help set the range. She said day 2 on out, calibrate every 12 hours unless the numbers were “way off”, then you should calibrate to get the readings back in line.
My first sensor, readings a little “wacky” at times. This one, more accurate - I calibrated 3 times the first day, I think 3 times the second day, and only 2 times today (day 3).

You definitely do not want to calibrate “too much.” There are times when I calibrate and the number seems that it does not respond - either it stays where it was OR actually moves FURTHER away from where I need it to be. However, be patient and it will come back. If in 15 minutes it is still off, then calibrate again. You don’t want to confuse the Dexcom by entering too many numbers. I have made this mistake several times. However, I do agree that calibrating MORE throughout the first day is good. By more, not every 10 minutes, but maybe every 3-4 hours as suggested.

Calibrate only:

When it asks you to OR

Your numbers are off by more than 20 points (50 seems a little drastic) OR

You know you will be unable to calibrate in the near future

I’m new the the Dex (3 months or so) and love it! My readings are soooo accurate. I always use my arm and love it! I’m so shocked the Dex isn’t approved for arm use because, for me at least, the abdomen is useless. The adhesion wears off before day 4, readings are NOT reliable, and it is very irritating and “itchy,” The arm site is out of the way, I never realize it’s there, and 95% of the time the readings are within 10 points.

However, just be sure to calibrate properly. Entering too many readings too soon should be avoided.