Anyone have a problem with their Dexcom tending to give lower than meter readings regularly? I’m not sure if it’s just my body’s interstitial fluid not cooperating or sensor placement, but the past few sensors keep reading a bit low, often alarming me to lows when I’m in the 90s and 80s. The first couple sensors I used were ok other than the first day when they were getting used to me. So far I’ve done the back of my arms (my left gave good readings, going back to that one today) and I tried my thigh. Do some placements give you more accurate readings than others? Could a whole box of sensors be “off”?
If it's consistently low (or high), then it's just a matter of calibration. You may be calibrating while your sugars are not level, and because of the delay in between interstitial and blood glucose, your readings won't match perfectly. I find that few calibrations, and only entering them when I'm level, helps with this.
I've recently started to only enter my BG readings when my Dexcom asks for them. This has really helped to get my BG monitor and Dexcom more in synch with each other, and as Andy says entering them when level helps.
I find the dex works great when BGs are in normal range. I get big discrepancies when BG is high or low. many times the dex is alarming me I am 60 or below and I test 80-100. Oftimes the dex is well in the 25 plus range and I am 50 or so points lower. I agree with Andy with regard to calibrations.
I find my Dex reading is routinely lower than my meter but never more than the 20% that is allowed. I don't think sensor placement is a big deal and I have worn sensors from top to bottom and had good readings wherever it's stuck. Calibration is a really big deal and can definitely lead to less than optimal sensor accuracy. I try to only calibrate when Dex asks or when it's off by more than 20%. I don't expect Dex to perfectly match my blood glucose meter because I know it's usually 10-15 minutes behind actual and if it's rapidly changing there is no way for Dex to realistically catch up. I just use it for the trends and invariably if Dex shows an up or down arrow my blood sugar will be heading in that direction soon enough.
My most important tip: Just because the Dexcom asks for a calibration, does not mean one has to be entered. It will continue to work just fine without it. I feel that much frustration I see written here is from people over-calibrating, because they assume that more is better, and ultimately end up entering numbers that are inaccurate because they aren't level. I only enter the initial calibration when I'm level, and don't enter any more until my standard glucose meter indicated that the calibration has drifted, usually only after several days of use.
For example, if Dexcom says I'm 100, and my meter says 95, that's close enough, and I won't enter the number for calibration. If I did, especially if there's insulin kicking, the Dexcom tends to spit out an even lower number, say 85-90, and is now calibrated less accurately. By entering more calibrations, it's only less accurate in this case. This may be counter-untuitive, but 4 years of experience has shown this to give the best results for me.
I do try to calibrate when things are level but maybe I will try skipping it altogether as Andy suggested when things are looking good, I wondered if that was ok. When I first starting using it a couple months ago I thought it was very accurate and I used sensors for about 2 weeks before they got a bit wonky, but the past couple sensors seemed off by more, probably user issues and not the Dex. I guess I thought after using it longer I’d get better at it and get even better results, perhaps I need to recalibrate myself and see what I’m doing different!
this is so helpful..thanks for your knowledge!
I sometimes have my Dexcom results read more than my One Touch Ping. My Ping is fairly accurate as it does coincide pretty well with the lab results. The Dexcom and the finger sticks are usually within a few points. The only things I find annoying are the ??? I get when exercising and inaccuracy when blood sugars are high.
My last Dexcom was the Seven and it woke me up all the time in the middle of the night telling me my blood sugar was low when my finger stick was in the 80s or 90s. I would pay attention to it if it was giving me a downward arrow - but most the time it was flat....So I am so delighted that the G4 does not do this.
Just one note of knowledge: BG Meters are known to be very inaccurate. Certain brands also have a known problem of reading too high at certain levels. My advice, keep doing what you are doing and let the A1c test be your final judge as to what's good or not.
Wow. How long can you go without calibrating? I think I too have noticed that you can go a while without elaborating, but I also think with the new SHARE Dexcom that I just received, the SHARE feature stops if it isn't calibrated when it says to calibrate. . .but I;m not CERTAIN if that is the case or not.
It's kind of funny. . as you can see from the chat on here (and from my experience with a sensor in for 22 days now), clearly you don;t HAVE TO do exactly what they tell you - calibrate every 12 hours and change sensors every 7 days!
If I really question a BG reading, or if I simply do not have a meter handy when it asks to be calibrated - I will sometimes 'create' my own calibration number based on what I THINK my actual blood sugar is. I have actually found this practice to be helpful.
A1Cs can be misleading too. I was having numerous lows for a time. Then subsequent very highs. ( On the roller coaster ride that we dread) My aic was 6.1. My actual average on my meter was 155 as i sometimes do not record the very lows because I am treating them.
Have you called Dexcom about this? It is absolutely possible that a box of sensors could be bad - I have had one where I had a lot of low readings. If it's far enough off - especially if it's repeatedly, they'll want to know and may replace the sensors.
That said, I find that Dexcom is routinely 'low' for me in I am feeling even slightly dehydrated. I assume that interstitial fluids drop and the sensor has less to sample, but I don't really know - only that drinking some water and waiting results in Dexcom 'catching up'. If it's very 'off' on any other time, I try re-calibrating it, which generally fixes the problem, unless the sensor is in fact bad.
I looked at the Lot #s and all three boxes are the same so it’s not the sensors Thav, however your point about dehydration possibly affecting readings is very interesting. I lost my thirst sensation years ago and have to remind/force myself to drink. I’m going to be more mindful of drinking water, it makes sense that “dried up” body tissues could maybe mess up the accuracy of our Dexcoms, we shall see, thanks for the suggestion!