New Dexcom G5 does not require finger sticks for treatment decisions (outside the U.S.)

Continuing the discussion from Dexcom G5 Approval by FDA:

The quote below is from the link in the quote above from LizBa’s post in the other discussion. Frankly, I don’t understand what the heck Dexcom is saying. Is it that as long as you continue to calibrate your monitor then you can use the Sensor Glucose (SG) from the monitor as the basis for a decision about how much/little insulin to take?

But Dexcom is clearly not saying you can stop using your BG meter only that you can use it less. Read the footnote in the quote below…

I frankly expected this statement to be dressed up with a lot more qualifiers. It’s not like Dexcom would advise people to insert a sensor, calibrate twice and from then on base their insulin on what the monitor says. Would they?

In addition, the new Dexcom G5 Mobile CGM system does not require confirmatory finger sticks when making treatment decisions.* The added convenience and cost savings associated with no longer performing finger sticks to verify readings on the CGM will greatly enhance the appeal of this integrated diabetes management system . The new device approved for use without confirmatory finger sticks* will initially only be made available outside of the United States.
*If your glucose alerts and readings do not match your symptoms or expectations, you should obtain a finger stick. A minimum of two finger sticks a day is required for calibration.

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Yes, that´s my understanding from what you have posted, @irrational_John.

I think Dexcom is simply following the same regulatory pathway that the Abbott FreeStyle Libre flash glucose monitor system pioneered with its CE stamp. That asterisk advised doing a fingerstick if your physical symptoms disagreed with the displayed blood glucose number.

***edit corrected misspelling

Sometimes I will bolus based off of just my Enlites (which works fine over 90% of the time) but sometimes I find out after I bolused that the Enlite was reading well above my BG. It hasn’t ever gotten me into a bad situation, but it does cause me a moment or two of butt-kicking. The better the Enlites have worked for me over time, the more I rely on the readings. If I have a sensor that is known to not be doing too well, than I do a lot of fingersticks for both bolusing and general bg checks. When they are wrong they are usually too low (from compression).

No matter how good any particular person’s experience has been with the Dexcom sensor, they still are not 100% perfect. Just from reading around the web it’s clear that even with the Dexcom there are still folks whose SG reading can still be significantly different from their meter BG reading.

I would have expected Dexcom to dwell on cautions about this more than they appear to have. And perhaps they will when the product is actually being shipped. And I expect they certainly will before the FDA is ever going to allow a similar approach in the U.S.

That’s all I’m saying. There is what happens to work for individuals and then there is what works for 99.9999% of all users. I expect the FDA will focus much more on the latter. And I’m more than a tad surprised that the regulators outside the U.S. don’t appear to have also done this.

I agree with this. It’ll be interesting to see how the development of the artificial pancreas proceeds regarding checks and balances to verify actual blood glucose. Perhaps it will ask the user to confirm when a significant insulin correction is considered.

I had a day one Dexcom sensor this week that was wildly inaccurate for the first 16 hours or so. Overall, however, the Dexcom is pretty darn good. I would have a hard time handing over fully automated control with the current CGM state of the art.

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Contrary to what we may like to believe, home-use meters are far from 100% perfect. According to this [2014 Diabetes Forecast article], to be approved for treatment decisions, here is the minimum accuracy a home-use meter must demonstrate:

For results at or above 75 mg/dl: 95 percent of meter test results must be within plus or minus 20 percent of the actual blood glucose level.

aFor results below 75 mg/dl: 95 percent of test results must be within plus or minus 15 points of the actual blood glucose level.

So, if your meter reads 65, the actual value could be anything between as low as 50 and as high as 80 (95% of the times). The reading could apparently be arbitrarily inaccurate 5% of the times?! My guess is that Dexcom is probably pretty close to being able to meet these pretty lame accuracy standards. Looks like they’ve met some European standards that may, somewhat arbitrarily, have slightly different accuracy language.

This is all primarily a legal matter - potential Medicare or other insurance coverage likely depends on the type of FDA approval.


Yes yes yes. I pointed this out on another thread. One of the things that’s been irking me about these discussions is that the fingersticks tend to get cast as the gold standard of accuracy when in fact they can be pretty far off in their own right, as @Dragan1–and a lot of others–have been pointing out. Obviously we don’t want to rely on something that’s worse, but it’s not a matter of abandoning certainty for the wild unknown. The fact is that we’ve been making these decisions based on imperfect data all along (what’s that? a fudge factor in the management of diabetes? Quelle surprise!).


I’ve written here before that it’s crazy that we dose insulin, a medication that can and does kill, with a very sloppy accuracy requirement. The real kicker for me is that the range is so broad (+/- 20 or +/- 20%) and on top of that they allow 5% of the readings to be whatever!

I think the manufacturers and their supporters think they’ve made a reasonable compromise between cost and our collective clinical experience. And that includes a huge quantity of people that do not use insulin. Just because it’s good for them doesn’t make them suitable for us!

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Well, from the anecdotal evidence that Dexcom in many cases does exactly match someone’s BG meter reading, then Dexcom already is, in many cases, “pretty close to being able to meet these pretty lame accuracy standards”. Huh. It’s a rare thing to be able to include both “lame” and “Dexcom” in the same sentence, no? At least in the DOC … :smirk:

While I am aware that accuracy and consistency requirements for my BG meter are officially not that tight, I have never really felt I understood what that means for actually day to day use. Being human, I just tend to take the number from my meter as my BG. What else can one do?

Also, just what does it mean if your Dexcom SG appears to consistently match your meter BG? Does that imply that the accuracy of your meter is actually much better than what is required? Or does it imply that the accuracy of the Dexcom is not all that great? :flushed:

Yes, I expect it would depend on that. But my point is that while this is certainly a legal matter, it is not only that, at least not for everyone.

Think back to any story you’ve come across from someone who, in hindsight, found out they got wildly inaccurate readings from their CGM. Now speculate about what would have happened if that person had not cross checked the Sensor Glucose against a meter BG but had just gone ahead and dosed based on the sensor value?

Should a regulatory agency just shrug off that possibility? If not, then what should it attempt to do to address this possibility?

My guess was that a much more extensive written warning disclaimer would be required from Dexcom. And while a disclaimer may well be pretty much only “a legal matter”, it still seems to be the standard way this situation is addressed. So I’m puzzled that it doesn’t appear to have happened. :confused:

Nothing. Personally, I routinely make numerous “therapeutic decisions” based solely on Dexcom sensor data but, as always, common sense applies: if the readings seem to be noisy or away from expected, check, and re-check with a meter. I just wish sensor and meter inaccuracies where the only problems we were to deal with!


I believe both home-use meters and properly calibrated Dexcom (I do not have any experience with other CGM) are indeed more accurate than the minimums FDA requires. Well, most of the time - there is inherent randomness in the sensing technology, not to mention user or other external-induced disturbances that affect the readings. So the best we can do is to be alert and use some common sense in interpreting bg data.

One thing that will mess up a finger stick reading is eating at Famous Dave’s, and not WASHING (wiping with a napkin turns out not to be effective enough) one’s hands of BBQ sauce that isn’t even visible. I did that twice over the course of several visits to FD’s. Thankfully my wife warned me to retest, and I also didn’t believe the result because it was higher than expected each time (WAY too high, given the time interval from the last test. this is all prior to me getting a CGM, so I used to test more than a dozen times a day). Retesting proved me to be far below the sugar-tainted results.

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Could not agree more. All these tools are amazing, but none of them are perfect. Meter, CGM, symptoms and common sense are all needed.

Having used Dexcom since the Severn Plus, I find dosing off of g4 to be completely acceptable in lots of cases. When Caleb was without a CGM, I had doubts about lots of meter readings and he would do an additional one to verify - even times when he would use a totally different meter. Having CGM and fingerstick (and knowledge and experience) makes for more informed decisions, better and easier management.

Inaccuracies often happen during the first day. I find that after the first day, it is fairly accurate within 10 mg.dl.