It woke me up, I looked and it was a low BG alert, it said I was at 40. I immediately got up went to the ref rig and gulp down an orange juice, then gobbled some additional carbs. As I sat down I started to think. My BG was around 101 when I went to sleep about 11:00 and hadn't eaten anything before going to bed. I got up took my BG with a finger prick it was maybe 10 minutes after the alert. My BG was 138 even though my Dex was reading 39 at that point. Thats 98 points difference. I know it takes about 2 hrs. for changes to BG to fully take place. I am convinced that by BG reading was way off on the Dexcom. What I have decided is to do a finger prick before taking actions. Has anybody had similar thing?
Always check the Dex before correcting. It can be dead on or WAY off.
I *always* do a fingerstick before taking action. Yes, the Dexcom can be WAY off....more so the 7+ than the G4. It can be off in either direction too.
It may be my imagination, but one of the things that seems to screw it up is sleeping with
the sensor pressed against the bed. I don't know if it is due to reduced circulation or what, but I have seen the (erroneous) very low reading you saw when sleeping on the sensor.
I always check my sugar levels to see if it matches the dexcom...if not I calibrated it just for safety measures. Always check the levels first before basal or fixing a low
I have had similar experiences although not as dramatic as 100 - alarm went off while I was sleeping saying 55 and my meter said 110 when I double checked right after the alarm went off. My dr advised me to always double check the lows with a meter reading. I find the low warning are accurate about 75% of the time. As HPNpilot said, I find that the dex 4 is more likely to be wrong about lows when I am asleep then awake, but I am not sure why.
I always check if dex says LOW. 9 times out of 10 I am in fact low or at least getting there but there is always that tenth time when the dex is off.
It takes a long time for dex to recover from a LOW so it will read 40 and a fingerstick will read 90-120. I always just recalibrate to the new number and the dexcom begrudgingly inches its' way up, but it is still another 15-20 minutes before it is reading "normal" again.
Thank for your responses. I have learned now to check with finger stick, part of the problem though is I was sound asleep and took awhile to get awake. Don C.
I have been off by 100 mgdl or more at times on Systen 7. I sometimes will treat a low without a finger stick, especially if I don't feel "right". I never treat a high without verfying with a finger stick. I bring you hope. On my G4, I have never been off 100 mgdl.
I used the Dex 7+ in 2010 and 2011 and had the same experiences. I was within 20 points of my meter readings about 50% of the time, but that is not good enough for me. My insurance stopped covering CGM's in late 2011 so I rarely use a sensor now, they are too expensive.
I have read that many Dex users have very accurate numbers the majority of the time, and others have very poor results. I don't know why it is that way. I always have to do finger sticks to check the Dex readings when it registers highs and lows.
I agree that lying on my side with the sensor pressed against the bed can cause poor readings. I also read that this is less likely for users who are light weight individuals.
Same thing happened to me last night...crazy readings while lying on my sensor.
If I lay on the sensor, or if I go to sleep dehydrated, it will go low on me at night.
If it goes low from laying on it, I get up and move around for a few minutes, drink some water, go back to bed, without calibrating, it is back on target within a half hour.
I think there is something about poor circulation either from being dehydrated or from compressing the skin where the sensor is, that causes it to not read correctly.
If I calibrate when it is in that state, it will always be reading high in the morning.
But, any time I get a low, even if I think it is because I was laying on the sensor, I get up and do a finger stick to make sure. No point in dying over a mistake like that...