First 24 hours with Dexcom

This is normally something I'd post as a blog, but I thought I'd do it in the forums so that people can lend thoughts and experiences. For those who don't know, I'm doing a Dexcom trial to decide if I want to buy one with my own money. I'll say up front that if my trial sensor lasts for two weeks there is no doubt that I'll be purchasing a Dexcom. :)

Here is my first 24 hours, which is actually not as bad as I thought it would be:

I seem to be having GREAT accuracy with the Dexcom. It is almost always within the same mmol/L as my reading, even if the decial point is different. And I've even had some match exactly:

Dexcom and meter both reading 5.2 mmol/L

In this first 24 hours I've also noticed some interesting things. I ate *exactly* the same breakfast and lunch yesterday and today (weighed and measured), and had the same routine both days, and got completely different results. (And since I know people will ask, no, it wasn't a low-carb lunch. I also pre-bolus by 30 minutes when I eat.) I plan on eating the same thing tomorrow (I'm also eating the same dinner each day) to see what happens, then after that I'll start experimenting with other meals.

Lunch on Day 1

Lunch on Day 2

Also, I've written before about how I think I spike in the morning from zero-carb breakfasts. But after last night, I think it might just be a rise that starts at 3-4am and continues until after 9am. This morning I ate a zero-carb breakfast and it didn't seem to change anything, eventually at 9am I was 10.5 or so and did a correction (I also did a correction yesterday after breakfast, before I'd started the Dexcom, so I don't think that contributed to my lunch thing...).

This afternoon I went low and I felt a lot lower than 3.8 (which the Dexcom said I was) and my meter said I was 3.1, so I had a glucose tablet. About 15 minutes later I was still 3.7 so had two more. Then another 15-20 minutes later my blood sugar suddenly shot up really fast:

Never would have thought 12g of carbs would make me go from 3.8 to 9.2! If that's indicative of how much carbs raise me (since there was no IOB at the time and I was not dropping fast) then a gram of carb equals 0.45 mmol/L or 8 mg/dl. However, last night I went low and I corrected with 20g of carbs, which I was sure would be too much but seemed to work perfectly...

Also, it seems like food and insulin both take forever to show up on the Dexcom, sometimes over an hour after eating before my blood sugar does anything.

Out of curiosity, how often do people see double up and down arrows? I was talking to a friend with Type 1 who says she rarely ever sees them. I've seen double up/down at least 5-6 times in the 1.5 days I've had the Dexcom...

Anyway, I am still only 36 hours into this experience. The rep said I can keep the receiver and transmitter until the sensor falls off - here's hoping that's at least two weeks! So far my sensor feels a bit pokey/sore but the readings seem very accurate and I think this could be a really, really useful tool for me!

(P.S. Sorry, not sure why some of the photos are upside down - they're linked to my Dropbox and the photos there aren't upside down, so not sure how to fix it...)

Wow, I have no Dexcom experience, although I think I signed up to get info from their website, it's hard to say for sure, as I haven't got much info. I guess they are in a good position saleswise and don't need to court new customers? That being said, I'm glad to hear your report that it's reading accurately and providing you useful data!!

But you must have plenty of CGM experience!! I just pre-bolused for dinner by 45 minutes nad so far it seems to be working perfectly!

Hi Jen,

I'm glad you have a dex trial and you're getting such good accuracy. For me it's variable, sometimes dead on and at other odd times completely off, I'm not sure why. But I would rather have it than not although I have been known to swear at my dexcom when it annoys me too much. I have had double up and double down, scary stuff, not too often fortunately and the last time it was completely wrong and crazy when I also had a pump issue of a missed bolus due to an occlusion. First dex said low 55 and then not too long after it said 170 double arrows up! I think that sensor was on the way out obviously. This one is getting wonky too, tonight it told me low 70 when I was really 110 or so.

This is from that night with the occlusion and the 55 then double arrows up 170, I can't remember what my bg actually was that night now.

That does look like it's jumping around a lot. All of mine have been very smooth so far, thankfully. It did do one jump this mornign morning when I calibrated (went from 5.2 to 6.9) but otherwise it's been great. It does seem like I'm lower than it says I am (i.e., it says I haven't gone lower than 3.8, but my meter said 3.3 last night and 3.1 this afternoon).

It was one crazy dinner because I'm so dizzy lately it is hard for me to tell from symptoms what is really going on so I had a test fest. That sensor was completely at the end though. They told me don't calibrate if you're moving up or down too fast because it will confuse it. Sometimes it does seem to right itself eventually and then I wait to see what will happen if I should change the sensor or not. But my bg was pretty stable it wasn't doing any of that.. it had a mild spike from the meal maybe.. I have to check my phone records to tell.

This one actually happened when I stupidly ate a low fat exact carb meal for the first basal test and the pump only bolused half of what I would normall take for it, even less prolly, it has rice, this was not fun.. I felt like I was going to have a stroke and I could barely think... this one was a true double arrows up to 289 from 110 in about 20-30 minutes or so.

Hope you are both having "fun" with the Dexcom. Better start saving your pennies because I predict you are NOT going to want to give it back. I have posted many times here about how amazingly accurate it is.

If you want to extend your sensor life as long as possible the KEY is sticking it down well. There are a load of posts on here with best practice (that's how I learned to do it) but to save time searching what I do is use Skin Tac and Opsite Flexfix (both available from Amazon).

Use the 4" (10 cm) wide flex tape, cut a piece around 6 cm (2.5") long. You need to cut a hole in the middle just big enough for the sensor bed to poke through. If you have an old sensor you can use it as a template. Lay the piece of flexfix across the sensor (with the cut edges up/down) - it should be just a bit larger than the oval tape. Fold it in two and cut out a hole just the right size for the sensor bed to poke through.

Swab area with alcohol wipe - let it dry off
Swab area with Skin Tac
Stick sensor in middle, insert the electrode as usual and attach the transmitter.
Now stick the piece of flexfix tape down over the sensor - the transmitter will poke through the rectangular hole you cut. (Manipulating the tape can be a bit awkward particularly if your fingers are sticky from the Skin Tac, but you can acquire the skill with a bit of practice.

I once had a sensor last 25 days and it was still firmly attached.

Jen: 3.8 to 9.2 on 12 g carbs isn't that surprising. The exact amount a set amount of carbs will raise your BG depends on bodyweight, but for a typical person expect 4-5g per 1 mmol/L rise.
I never see the double arrows - not even if I am very hypo and have eaten 20g of glucose tabs. However, it will depend on how quickly the sensor glucose follows BG and this depends on individual physiology. (I am also using my Vibe as a receiver which may make a difference)
Looking at your screenshot it seems like your red-line for low BG is set at around 4.0. If you are serious about hypo warnings you might want to raise that (you already had a case where the sensor was lagging behind your fingerstick). I set mine to alarm at 4.4.

Meee: your little excursion to 55 on the screeshot. Did you confirm this with a fingerstick? It looks to me like what I would call a "drop-out". This happens if the sensor temporarily loses good contact with the subcutaneous tissue. I see these typically when the sensor is getting towards the end of its life but if you don't have yours well attached you may see it earlier (or your physiology may be different to mine).

Having a sensor attached makes you realize how many things can radically affect your levels.

Best of luck


Jen - I wish you the best of luck with this Dex CGM trial. It's been a valuable tool and a continuing source of learning for me.

How are you doing allergy-wise with the adhesive? Did you use any additional adhesives?

I look forward to reading about your experience.

It sounds like you're getting a lot of good info!
At the very least, maybe you'll have time to tweak your basals for the dawn phenomenon. I've noticed the rise starting 3-4pm too. The Dexcom has been wonderful for seeing how small insulin tweaks affect things.

As far as the double up arrows, they do happen sometimes for me. Not too often - just enough to get my attention when it happens. Single up arrows are far more common. (A flat line is just a daydream for me…) But I think it comes along with the territory of moderate carbing. And when you factor in that we have additional restrictions with the food allergies, that makes food choices a bit tougher. So any day that I can keep myself almost completely in a healthy range is a win. The Dexcom makes those days happen more often - whether it's just a good day or the ability to correct early when numbers start getting wonky.
If you're getting double arrows while sleeping, keep in mind that sleeping on top of the sensor can really affect the readings.

Hope the trial works well for you with no allergy issues.

Meee, that is a very odd looking G4 graph. I've never had anything like that -- smooth, no discontinuities -- except from calibrations that are way off.

Is that what all those sharp jumps (up/down) are? Calibrations?

If so, you're calibrating WAAAAAYYYYYYY too much, which could be part of the accuracy problem you're seeing.

If not, then something else is wrong. I've gotten somewhat nonlinear results when I've had bad sensor insertion or placement. I find the backs of my arms work best for me in terms of accuracy, sensor life (always get 2 weeks there).

With the new firmware released recently, I can often go 24h without calibrating, and when I do, the dang thing is still within 10mg/dl.

I'm not convinced that it's simple YOU -- i.e. some novel Meee biochemistry that doesn't work with the G4 (if so, apply to make $$$ as a research subject!). I'm not giving up yet that your D family can figure this out.

Day two - exact same food and schedule as day one. Even when I did corrections was the same after breakfast, though I didn’t correct after lunch or dinner on day two. I’ll do another “same” day and then start experimenting!

Thanks for the tape suggestions. I have a local T1 friend who uses the Dexcom and keeps sensors in for 2+ weeks, so they cut a piece of some heavy-duty tape they use. I stuck it on yesterday and it seems to stick really well - but even the Dexcom tape is sticking well. The sensor has not felt like it's shifting around at all, even though the transmitter is bulkier than I thought it was.

Last night I went low and ate 28 grams of carbs. (I over-treated: Dexcom woke me up out of a dead sleep when it said I was 3.7 but my meter said I was 3.1, and Dexcom says the lowest I got was 3.3, while I went down to 2.6 according to my meter. I definitely will be raising the low alert level!) Anyway, with that many carbs I only went up to 9.5 or so, which is about half of the rise from carbs earlier in the day. For now I am just observing and not trying to modify anything that I do, but this is the sort of thing I'm hoping Dexcom will help me sort out...

The sensor is a bit pokey/sore feeling, sort of like the metal infusion sets feel like for me, but the infusion set I have on the other side of my stomach is itching me and the Dexcom doesn't feel itchy at all, so I'm taking that as a good sign! I did get some additional tape and used that to stick it down, so here's hoping it lasts two weeks or more. I really feel like this could change my life.

So far no double arrows during sleep, only when I eat (double arrows up) or do a correction (double arrows down...if it goes down...).

The weird part is that this morning I didn't rise at all. Although I did do a correction after breakfast (I was high from over-treating a low around 11:45) that did basically nothing, so maybe that was a hidden rise. I did go low both nights between 11 PM and 12 AM, though, so that alone is good info as far as I'm concerned! I suspected I was going low at night but whenever I woke up to test at 1 AM to 3 AM I would be in range, I didn't think that it might be happening shortly after falling asleep.

Also, if there's anything that would persuade me to try low-carb as much as I can (I'm currently not even trying - just counting the carbs I eat) it would be the Dexcom. Already I can see that the zero-carb breakfast I eat causes no rise at all, while all the other meals do. Tomorrow I'll try eating a dinner that's 20g of carbs or so and see what that does.

Please keep posting. I'm enjoying your analysis. I hope your sensor lasts a long-time!

Know nothing about Dexcom, but I try to keep up with your posts, Jen, and I just wanted to say Hi---I'm here! ever, Judith in Portland.....

Hi Dave, the first one the sensor was really on the way out, or already out... I may have done 1 calibration then because sometimes it calms it down and I can get good readings again after but normally I only calibrate when it asks me to or when it is 30 points or more off, according to dexcom help, and I actually frequently have readings that far off and more off. It has trouble often when my bg moves quickly or when I eat or take insulin.. lol. The other graph, there were no calibrations done that was what actually happened, except my finger stick was 289 at the highest. I was just trying to see if I was getting any insulin at that point, on the phone with tandem etc. My sensors are all placed in my stomach/abdomen area now and I've had no problems with insertion etc. I had tons of problems with the last dex(earlier model) and sent it back. I may just be one of those people who it doesn't work as well for, but any help you guys can give me is great. If dex pays me I will maybe apply for that, lol.

btw for that spike I did a 2 unit correction with 3 units or so on board.. should have done 2.5 but I was being cautious. My endo had put different settings in for everything as I transitioned to the pump and did testing which was part of the problem. Mee.. entering the dexcom twighlight zone area :-)

Jen, I forgot to say that is good if you're really lower than the dex. I do find for me it is usually about 10 points off on average, but most of the time the trends are right. Although it has missed some lows for me which I caught with symptoms. I'm terrible on mmol so I'm not going to try to comment on your numbers. I think the dex is going to help you a lot though :-)

I think this is a good start! you can start to really see what is going on when you eat, for me the spike seems to come later, depending on what I eat and bolus etc. sometimes I will correct a tiny bit on the pump when I hit 140's but I have to be careful because that can drop me low too.. or I can end up high for hours if I don't. I can't believe how much you went up at 12 am!

the first time I saw a double arrows down was when I was driving home from work, I was in the 160's after a correction, but it scared me a lot because I can drop very rapidly from there sometimes.