How accurate is your Dex?

I just started on the Seven+ on Friday. I am finding that what Dex shows and what my meter shows are, for the most part, very different. I was just wondering how other Dex users numbers are? Is this something I should worry about ?

Could be a defective sensor and/or poor site (to close to muscle). This has happened to me a few times. Contact somebody in customer service and explain the problem. They will likely have you send the receiver data to them so they can analyze to see if it should be replaced free of charge. I give customer service high marks at Dexcom when it comes to this.

The longer the sensor is on the more accurate it becomes also the more sticks you enter into I enter every stick I do into it also accuraccy has to do with the site healing up were the sensor is inserted thats what my my trainer told me I my first sensor just errored out tonite after 11 days of use after 2 days it was real close to my meter the higher ranges are usually further apart then the lower ranges I love me sexy Dexy even after only using her for 11 days !! Hope this helps! RenZ

My seven+ is pretty accurate most of the time. It depends on how you define accurate though, hahaha! If the transmitter and my glucometer are within 20 points or less of one another, I consider that close enough to accurate. Sometimes they are within a point of one another. I am still learning the subtleties of the setup since I have only been on it a little over a month now. I had to get over the idea of the glucometer and the receiver having the same numbers, that is not what the dexcom is for, it is more about trends.

Make sure you don’t calibrate the system when your sugar is rapidly changing, it really messes up the accuracy! I know DexCom says you can calibrate at any time but if I am dropping rapidly or spiking after a meal and I put that BG in, my system is way off for hours. I found that if I have to calibrate when my sugars are swinging that if I put in 2 back to back readings in the receiver, this helps with accuracy for me. I might be imagining this but I swear this can help if you are forced to calibrate when your sugars are changing alot.

I enter every BG I take into Dexy she likes it that way it makes her more accurate over time and shows the full trends with sticks to compare to

OF COURSE you should worry about this. (All that money, all that trouble, and useless readings.) What location are you using, and have you tried others?

I’ve got it on the right side of my stomach. Have not tried any other sites other than the stomach. Can I use my arms…etc like I do whith my Omnipod?

Hi, I have the same issue with my dexcom…any advice? Sometimes off by like more than 100 points!

Right about the site healing up, but wrong about the “more fingersticks” guess.

The first day, or so, is much less stable than following days. There’s a small initial “pulse” of reagent burnoff, plus a small “break-in” of voltage differentials along the signal path under body-mounted conditions. But far more important a factor is the damage, only at an invisible microscopic level, which is caused by Sensor insertion. At this microscopic scale, the tissue damage is substantial, and the “ISF fluid” which gets to the Sensor isn’t really the standard for which it’s built. (There will ALWAYS be a bit of blood, even if you don’t SEE a major episode of “blood-poisoned Sensor” disease.) Tissue-repair chemicals, and byproducts of the repair process, are also present at heightened levels.

If a Sensor is treated correctly (with absolutely no subcutaneous movement subsequent to insertion), then days 2-5 will be the best. They’re followed by a long, slow decline in accuracy. More fingersticks are good, but ONLY if they’re entered under stable bG conditions. Although Dexcom will normally be pretty closed to measured bG during a period of falling bG, Dexcom readings will be “behind”, by varying amounts of time 10-30 minutes, in rising bG. So, if you calibrated from fingerstick during a period of rising bG, Dexcom has been given bad data, and the calibration will become skewed.

Also, I think that it’s a bad idea to EVER calibrate above 200 mg/dL or so. Dexcom bahavior is not totally linear, so the adjustments which it’s going to make when it’s fed data at extremely high bG are going to lead adjustments which hurt lower readings. And the place where accuracy becomes critical isn’t up there anyway-- you shouldn’t feed it a lot of calibration numbers to fix readings above 250, 300 mg/dL to be within 5% or 10%, because those calibration adjustments are likely to increase error in the critical ranges. The critical range is below 80 mg/dL.

When your reading is off by a lot, say 1/3 at reported bG of 300, it isn’t a huge, immediate problem: whether you’re 200 or 400, you’re high, and you’re at least doing the right thing even if you’re not doing exactly the right amount (i.e., of add-on “correction” insulin.) And there’s plenty of time for finger sticks and back-filling with food, or additional adjustments, over the next 2-3 hours.

But if your reading is 81, and you’re actually only 55 or so, you’re already stumbling around with the reaction speed and mental acuity of someone dangerously drunk, and you could be unaware of it-- or decide not to treat at all, because “it looks OK, and I calibrated earlier this morning”. If you’re driving a car, or using dangerous power equipment, it’s the equivalent of multiple martinis. (At my weight, about FIVE martinis, all together, without food. Roaring drunk.)

Lows need MORE careful care than highs. This is because, unless your infusion set or pump has totally failed and you’re flying towards Ketoacidosis, highs are not immediately life threatening. Lows can become life-threatening very quickly, usually via accidents.

Now, with all that talk out of the way: it sounds to me like you’re doing an AWESOME job of handling your “sexy Dexy”. My own is always either dressed in basic black, or totally naked. Kinda sexy both ways, as long as “she” doesn’t get into one of those hissy fits of buzzing, vibrating, screaming, and complaining about something I did (or didn’t do). But compared to the other sexy people visiting the house, or living here, my “Dexy” is definitely kinda high-maintenance. But, I just can’t seem to live well without her!

Definitely DO NOT EVER calibrate when bG is rising. Gory details follow:

Dexcom is often very close at tracking falling bG, because your cells are sucking sugar (for energy) out of ISF faster than the “suckage” gets from “starved ISF” back, to be noticed by a bG meter, into your 5 quarts of blood. (In falling bG, the ISF glucose falls quicker.) But it also takes time for falling ISF bG to “soak into” the Dexcom’s titanium cover and create low readings. So in the falling direction, what happens with Dexcom for a lot of people is this: The two delays cancel each other out, almost perfectly, and Dexcom ends up reporting a nearly perfect match for fingerstick BLOOD readings as you go down.

If you’re such a person, and the rates of fall is matching in exactly that way, then readings promtly entered as calibrations during periods of falling bG will be “good” readings. This is not true with Minimed, and I don’t know why. Minimed seems to be about 15 minutes “late” in both directions, while Dexcom is “late” only in the upwards direction.

But for me, upwards is also a lot worse than 15 minutes: After a too-big feast of carbs with inadequate insulin, the two delays don’t cancel each out-- they become additive.

Rising bG hits the blood first, directly from your stomach (with some sugars); almost directly, but a bit later, through your intestines; and finally, form your liver. All bG hits blood first, and then circulates into ISF and cells. The “ISF-versus-blood-delay” is about the same length of time as before but this time it isn’t cancelled out by Dexcom reading from ISF-- rather, late becomes “even later”, the two delays pile on together, and Dexcom is vastly late, entering a calibration is definitely a mistake.

By the way, your idea to “Clean it up” by typing in MULTIPLE calibrations entries, one right after the other, at identical or nearly-identical bG values, definitely works. Here’s why:

One of the biggest changes between Seven+ and it’s predecessors is in calibration: the “+” now gives calibration readings much greater “weight” in the formula than old ones. With the original STS, Sensors officially died after only 3 days, calibration data was never more than 3 days “stale”. But with the original Seven, all of the readings subsequent to the last start-up are used with equal weight. (Mistake!!! no matter what kind of line you TRY to fit, the data from an almost fresh Sensor full of unused reagent can’t be matched up properly with data from day 6, which WILL give much lower levels of raw voltage for the exact same bG readings.)

So, when you enter a handful of bG readings all together, instead of just one, they cause old, “bad” readings to be discounted by greater and greater amounts. Pretty soon, they count for next to nothing. :))

BTW, if you still use a cable, THROW IT OUT. Uploading from One-Touch seems to get into a software problem where the “importance” of old readings is brought back up to the time that they are re-sent, not the time they actually occurred. And since OTU tries to upload everything it has, that completely destroys the advantage of the new “discount stale readings” software, behaving just like the older non-plus “Seven”. Always enter via the keypad, and never enter during periods of rising bG.

If it starts creaming for “enter fresh calibration!” during an upward trend, just IGNORE IT. Just let it scream. if your bG keeps flying around, leave it screaming all night. Don’t be convinced to enter anything until you’re a solid, steady “flatliner”, or even falling slightly. It’s far better to leave it working from 18-hour-old GOOD data than it is to create a mess by entering BAD data in response to the screaming display. Just say No!

We just stared DN’s first sensor. Dex Rep did not like area she chose to wear it, but DN does not want to wear on arm/stomach because of bathing suits. So any problems might be due to placement of sensor. When her BS is stable (no insulin or food digesting), sensor is accurate. It has been inaccurrate when eating (alarming for low and she was 160) also high alarm beeps at 160 and she is already 220. So it will take a while for us to get the hang of it. She spikes high and fast after eating, so we will definitely have to prebolus ALL meals, not just breakfast. We slept through high alarms. Have to get her wireless mike hooked up. Dex just vibrates and gives two short beeps, does not keep beeping like Minimed. So thrilled that the insertion process was virtually painless. That was our main gripe with Minimed sensors. She will be able to wear it, since it does not hurt. Hope to figure things out within a week, month or so. Love the Dex.

Good, you’re ALREADY learning about high-bG events which you didn’t even suspect before adding Dexcom! (I.e., how fast and high she spikes during and immediately following meals).

For most people, Dexcom is nearly always very “late” in tracking increasing bG. But alarming “low!” when she is at 160, that shouldn’t happen with a good Sensor. Was she sitting on the Sensor? When butt-cheek-located Sensors are inserted too far down, and the wearer sits down, both blood flow into the area and flow of bG into ISF gets disrupted by all the pressure. (Sitting on, or nearly on, your butt-mounted Sensor stops the local blood flow. Even though the big arteries don’t become totally squashed down, the tiny capillaries and small feeding vessels right next to the Sensor DO get squashed, and blood flow decreases dramatically.)

Cells around the Sensor continue to absorb Glucose from the “local” ISF for energy, but that ISF doesn’t get Glucose replenished by blood (because the blood flow is curtailed, and local blood is similarly “sucked dry” already). AFAIK, that’s about the only way a “good” Sensor can give a badly erroneous “low” reading. The same error can occur by rolling over and sleeping on it; do not automatically feed an in-bed “low alarm” without checking bG to make sure that it wasn’t one of these “squashed location, stale ISF ran out of Glucose, but only locally” incidents.

For most people, Dexcom is much better AND much less delayed in tracking downward bG movements than it is at upward bG movements. But that 160 versus 220 is normal for such a strong and sharp spike. pre-bolus helps, but pre-loading fat and/or reducing the carb load might be even better tactics to avoid those spikes.

pre-bolusing is certainly called for, and maybe the carb/fat/protein balance needs to be addressed too. When a meal is going to be carb-heavy, I try to load up the fat first (salad oil, nuts, or cheese). Or, I drink wine, by itself, before the carbs start-- so that the alcohol-provoked drop in bG counterbalances the sudden rise form the carbs. But the timing of that balancing act is very sensitive, I often need to lunge for sugar tabs in the middle of the meal if I miss it even slightly.

Pre-bolusing will help match the timing a bit better, but for most people, no amount of timing can match the sudden, really strong surge which a carb-heavy, low fat meal will create. Pre-loading some fat, or largely switching away from such carbs entirely.

For example: Mashed potatoes. It’s just a pile of useless, empty calories (until you add a bunch of really unhealthy, saturated fat stuff to MAKE them taste like something.) Unless you need empty calories to gain some weight, just let 'em go.

Mike, try your love-handle first: Straight down from the armpit, above the beltline and below the first rib.

The performance difference may be huge: Frontal pecs have far more movement in everyday life-- even at the edge (as little as a single inch away from the muscle group I’m recommending.)

Let me know how that works for you.

Nilufer, please see “love handles!” which I just wrote for Mike (immediately above).

We had tried Minimed sensors with my niece and they were a pain, plus inaccurate a good deal of the time. Just started the Dexcom and I think our readings are great about 70 percent of the time. When BG is rising rapidly or dropping quickly (when you have the arrows), I do not find Dexcom is in range with the fingerstick. However, whenever we see one of the up or down arrows, we do not expect them to match because there is a quick rate of change. Just seeing the directional arrows will guide us. For instance post-prandially, if we see a lower BG value than it should be at the time, with a down arrow, that will signal to us that she may need more carbs. Up arrows at night, we check, give correction and will add a temp basal on top of the correction. We are still newbies and feeling our way around. I’m sure we will get the hang of it within a month. I do not expect BG numbers to match all the time or be close; fortunate to have the trend arrows, for times when BG is changing rapidly.

GREAT suggestion…Thanks. I think I’m hooked. The accuracy is almost spot on !

Rickst29 So never enter data into Dexy on the upward trend? Just test and bolus and wait for Dexy to give a flatline straight arrow? Then test and confim and enter new dtat finger stick into Dexy? So Do Not enter every finger stick into Dexy?

Yes, exactly!

NEVER perform “enter bG” during a period of rising bG. Just don’t do it, it wrecks the calibration curve.

Thanks for the reply, I love to hear about good outcomes. :))

It’s too bad that Dexcom can’t afford to have this alternate site area studied for FDA approval-- because for most adult men, it’s WAY better than the official frontal abs. (Too much muscle movement, mostly from regular breathing.) But without the $$$$ study data, Dexcom support can’t bring up the “alternative site” suggestions on their own, or put them in the User Guide.

Their talk, as well as their documentation, is regulated by the FDA rule that “As the manufacturer, you can’t talk about off-label things.”(Fortunately for US, I’m not a Dexcom partner or employee-- so I can speak and write quite freely.)

You can go about an inch-and-a-half forwards, plus about an inch backwards, from the “absolute” middle of the curve along your side. There’s also about an inch-and-a-half vertical area between “too close to belt” and “too close to ribs”.

So, for me, and probably for you, this allows about 6 needle locations, separated from each other by more than on inch, on each side. Even at only 10 days per Sensor, that’s almost 4 months before you need to poke REALLY close to an old site again. (For me, it’s well over 6 months).

You should hand draw a chart for this and then run it through the copier to keep a “clean” spare for the next chart. Each time you poke in a site, mark the start date at each of the locations you use (the needle location, not the pad) so that you avoid getting too close to each one, in re-use, for as long as possible.

So do you think it adds to Dexy’s accuracy to add additional BG entries if they are added @ the proper stable even arrow times?? Like to add more reading then just when she asks for calibrations or every 12 hrs is all she needs? I was under the impression more BG’s = more accuracy.