# Dexcom time lag, and interstitial fluid glucose vs BG **URL:** \ **Category:** C/GM\ **Tags:** blood-sugar\ **Created:** [October 10, 2017, 8:12pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318 "2017-10-10T20:12:51Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MM2](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/mm2/32/3032_2.png) [@MM2](https://forum.fudiabetes.org/u/MM2)\ **Post date:** [October 10, 2017, 8:12pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/1 "2017-10-10T20:12:51Z")
One thing that was never clear to me, is what does dexcom do regarding lag of tissues vs blood glucose. So is the value that is displayed on receiver what dexcom projects is blood glucose right now, based on tissue glucose that sensor filament is measuring plus trend. ?? I have seen comments suggesting display value is based on current tissue glucose measurement, so wait 15 minutes to see a value that should match closer to BG meter. And for those using xDrip, what does it report ?. ---
**Author:** ![Michel](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/michel/32/387_2.png) [@Michel](https://forum.fudiabetes.org/u/Michel)\ **Post date:** [October 10, 2017, 8:13pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/2 "2017-10-10T20:13:56Z")
This topic was split from: > [@How your Dexcom CGM reacts to calibration input](https://forum.fudiabetes.org/t/how-your-dexcom-cgm-reacts-to-calibration-input-soliciting-feedback/2293): > > When you enter a calibration value into your Dexcom receiving device, your Dexcom data does not automatically line up on the new value. it is easy to understand why. The measurements from a manual glucose monitor are only specified to be accurate with +/- 20% – an awfully poor expectation, but seemingly the only one that allows a reasonable cost for the strips used to read a BG value. On the other hand, your Dexcom, over time, averages out many cali… ---
**Author:** ![Michel](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/michel/32/387_2.png) [@Michel](https://forum.fudiabetes.org/u/Michel)\ **Post date:** [October 10, 2017, 8:43pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/3 "2017-10-10T20:43:27Z")
> [@MM2](#): > > So is the value that is displayed on receiver what Dexcom projects is blood glucose right now, based on tissue glucose that sensor filament is measuring plus trend. ?? What I thought until you posted your question: - The glucose level in the interstitial fluid is 10-20 minutes behind the BG - calibration matches the interstitial fluid glucose to BG, but does not remove the delay - the Dexcom shows a number that is 15 minutes behind the real BG. I was going to post in that sense, but I actually reviewed some scientific literature, and, as of 2014, the papers are saying that the Dexcom number is estimating the BG right now (not 15 minutes behind). I am not 100% sure what is reality today. I need to do more research 🙂 > [@MM2](#): > > I have seen comments suggesting display value is based on current tissue glucose measurement, so wait 15 minutes to see a value that should match closer to BG meter. I had always assumed that was true (and somewhat verified by experience) until you asked 🙂 > [@MM2](#): > > And for those using xDrip, what does it report ?. I am pretty sure that xDrip reports the BG 15 minutes ago, as estimated from the interstitial fluid. But confirmation should come from the experts: @docslotnick, @dm61, what do you think? ---
**Author:** ![docslotnick](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/docslotnick/32/75_2.png) [@docslotnick](https://forum.fudiabetes.org/u/docslotnick)\ **Post date:** [October 10, 2017, 8:56pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/4 "2017-10-10T20:56:58Z")
Not exactly sure about the xDrip algorithm, but I rarely if ever get a fifteen minute (or five minute) lag when crashing and recovering. The readings stay pretty consistent with fingersticks going into and coming out of a low. ---
**Author:** ![Eric](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/eric/32/9209_2.png) [@Eric](https://forum.fudiabetes.org/u/Eric)\ **Post date:** [October 11, 2017, 3:00pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/5 "2017-10-11T15:00:41Z")
I’ve never really understood how they do it. This morning I was 55, and I quickly brought it up to 87 (within 10 minutes), but the CGM was still showing me in the very low 60’s after 56 minutes (with a horizontal arrow). I don’t get it. After 56 minutes it still hasn’t caught up, and shows no inclination of catching up. ☹ ---
**Author:** ![CatLady](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/catlady/32/36_2.png) [@CatLady](https://forum.fudiabetes.org/u/CatLady)\ **Post date:** [October 11, 2017, 3:17pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/6 "2017-10-11T15:17:48Z")
> [@Eric](#): > > After 56 minutes it still hasn’t caught up, and shows no inclination of catching up. ☹ Have you ever asked the Dexcom tech support folks why this happens? ---
**Author:** ![Eric](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/eric/32/9209_2.png) [@Eric](https://forum.fudiabetes.org/u/Eric)\ **Post date:** [October 11, 2017, 3:45pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/7 "2017-10-11T15:45:17Z")
> [@CatLady](#): > > Have you ever asked the Dexcom tech support folks why this happens? Yes. Apparently my body tissue is not ideal for CGM. Snips and snails and puppy dog tails, and all of that. ---
**Author:** ![docslotnick](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/docslotnick/32/75_2.png) [@docslotnick](https://forum.fudiabetes.org/u/docslotnick)\ **Post date:** [October 11, 2017, 6:35pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/8 "2017-10-11T18:35:48Z")
> [@Eric](#): > > Apparently my body tissue is not ideal for CGM @Eric Looks like we need to fatten you up 😉 ---
**Author:** ![Eric](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/eric/32/9209_2.png) [@Eric](https://forum.fudiabetes.org/u/Eric)\ **Post date:** [October 11, 2017, 6:52pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/9 "2017-10-11T18:52:05Z")
Trying. Last night: ![IMG_2350](https://canada1.discourse-cdn.com/flex030/uploads/fudiabetes/original/2X/e/e47572899c221d71d6c4590e853f9fb01d4d84eb.JPG) ---
**Author:** ![docslotnick](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/docslotnick/32/75_2.png) [@docslotnick](https://forum.fudiabetes.org/u/docslotnick)\ **Post date:** [October 11, 2017, 7:03pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/10 "2017-10-11T19:03:45Z")
@Eric Those 35g of carbs won’t do anything. I hope you at least had some flan covered with whipped cream for dessert. ---
**Author:** ![Michel](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/michel/32/387_2.png) [@Michel](https://forum.fudiabetes.org/u/Michel)\ **Post date:** [October 11, 2017, 7:12pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/11 "2017-10-11T19:12:36Z")
> [@docslotnick](#): > > I hope you at least had some flan covered with whipped cream for dessert. This was a wonderful laugh, sorely needed on this end, thank you @docslotnick! ---
**Author:** ![Eric](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/eric/32/9209_2.png) [@Eric](https://forum.fudiabetes.org/u/Eric)\ **Post date:** [October 11, 2017, 7:14pm UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/12 "2017-10-11T19:14:40Z")
I had a pitcher of margaritas and actually sent it back for more tequila. They had a rookie bartender last night. ---
**Author:** ![Robellengold](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/robellengold/32/2082_2.png) [@Robellengold](https://forum.fudiabetes.org/u/Robellengold)\ **Post date:** [October 12, 2017, 12:47am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/13 "2017-10-12T00:47:20Z")
I asked tech that before they said it’s when the sensor gets blocked similar to when it eventually breaks after wearing a lot - the fluid gets stuck in the sensor with the same reading and stays flat even though it’s actually changing Same thing effects when you see a flat like and then it jumps to another flat line - sensor is getting clogged and unclogged not sure if he was makkng it up but he said to massage the fat around and it might loosen the block ---
**Author:** ![Sam](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/sam/32/10595_2.png) [@Sam](https://forum.fudiabetes.org/u/Sam)\ **Post date:** [October 12, 2017, 12:57am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/14 "2017-10-12T00:57:09Z")
> [@docslotnick](#): > > @Eric Looks like we need to fatten you up 😉 I’ve actually wondered about this… in my years on the doc it seems that I’ve observed on general that people with very lean body types report far less stellar cgm performance than those with maybe just a little tiny bit more body fat… I don’t even mean fat people either there seems to be a discrepancy between normal and extra lean people in my observation… not exactly a scientific experiment but I wonder if guys like me and Eric just aren’t juicy enough to keep the dexcom working right ---
**Author:** ![Michel](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/michel/32/387_2.png) [@Michel](https://forum.fudiabetes.org/u/Michel)\ **Post date:** [October 12, 2017, 1:02am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/15 "2017-10-12T01:02:08Z")
> [@Sam](#): > > I wonder if guys like me and Eric just aren’t juicy enough to keep the dexcom working right That’s what Dexcom asks me every time we have a wonky performance issue: “Lean body type? Oh, that’s why.” ---
**Author:** ![Sam](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/sam/32/10595_2.png) [@Sam](https://forum.fudiabetes.org/u/Sam)\ **Post date:** [October 12, 2017, 1:12am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/16 "2017-10-12T01:12:46Z")
Being skinny in the diabetes world can be a lonely place ---
**Author:** ![Michel](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/michel/32/387_2.png) [@Michel](https://forum.fudiabetes.org/u/Michel)\ **Post date:** [October 12, 2017, 1:14am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/17 "2017-10-12T01:14:49Z")
> [@Sam](#): > > Being skinny in the diabetes world can be a lonely place There are a whole lot of you. In fact, almost all the T1s I know are skinny. Of course, that would never include me 🙂 ---
**Author:** ![Eric](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/eric/32/9209_2.png) [@Eric](https://forum.fudiabetes.org/u/Eric)\ **Post date:** [October 12, 2017, 1:15am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/18 "2017-10-12T01:15:24Z")
Same for me, they always ask if I’m thin and kind of give an “oh…” response. ---
**Author:** ![Sam](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/sam/32/10595_2.png) [@Sam](https://forum.fudiabetes.org/u/Sam)\ **Post date:** [October 12, 2017, 1:18am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/19 "2017-10-12T01:18:56Z")
Their flow chart just dead ends there. If the answer is No there are like 200 other branches. It’s fit shaming. ---
**Author:** ![Michel](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/michel/32/387_2.png) [@Michel](https://forum.fudiabetes.org/u/Michel)\ **Post date:** [October 12, 2017, 1:43am UTC](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318/20 "2017-10-12T01:43:11Z")
> [@Robellengold](#): > > the fluid gets stuck in the sensor with the same reading and stays flat even though it’s actually changing That’s really interesting, @Robellengold: I have also seen this phenomenon before but never quite knew why. I wonder how accurate the answer is. It could be true. [Next page](https://forum.fudiabetes.org/t/dexcom-time-lag-and-interstitial-fluid-glucose-vs-bg/2318.md?page=2)