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 ?.
This topic was split from:
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 
I had always assumed that was true (and somewhat verified by experience) until you asked
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?
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.
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. 
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.
@Eric Looks like we need to fatten you up 
@Eric Those 35g of carbs won’t do anything. 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!
I had a pitcher of margaritas and actually sent it back for more tequila. They had a rookie bartender last night.
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
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
That’s what Dexcom asks me every time we have a wonky performance issue: “Lean body type? Oh, that’s why.”
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
Same for me, they always ask if I’m thin and kind of give an “oh…” response.
Their flow chart just dead ends there. If the answer is No there are like 200 other branches. It’s fit shaming.
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.
