Paradox.... help explain please?

Yes or no, the CGM readings must not be used for “immediate” insulin dosing?

Meaning, time for a shot/bolus you take the number off the CGM then you have to reconfirm it first with your own tester, before you can use/trust that number. That cannot be true… is it?


Absolutely true. You should never dose insulin based on a CGM reading.

The purpose of the CGM is to get a larger picture of your diabetes than what is provided by finger sticks alone. A CGM will help you fine-tune basals, see how different foods affect you, and prevent BG highs and lows.

Why is secondary confirmation necessary? Either the numbers it gives us are accurate/valid or they are not. It cannot be both ways.


None of the CGM manufacturers claim that their devices are 100% accurate 100% of the time. Moreover, it is well documented that values from testing interstitial fluid glucose are approximately 10-30 minutes behind values from blood glucose testing.

For more information, refer to the following study.

I have found that the DexCom system is more accurate than Minimed (I’ve used both).

I confirm before I take a correction dose. But, I also use the trending info it gives me to try and head off a low if I see it trending down rapidly and know I have IOB, many times, I’ll start a temp basal dcrease in those situations to try and prevent a low . This is only my third week with the CGMS, I’m still learning. It’s also helpful heading into excercise. It’s really helping me understand how my body reponds to insulin, food and activity.

I also use a dexcom, and have so far, found it to be very accurate. The only issue that I’ve found is, it takes quite a while to register an upward trend when I have a low, as much as 15-30 minutes later, it is still reading in the 60’s when a fingerstick shows I am in the 90’s. But it does catch up eventually.

Hello Shannon:

I appreciate your perspective and definate patience for contributing to my question(s). Given I do not use a pump, fine tuning “basal rates” would be totally worthless-irrelevent . As for the other aspects mentioned… why do you/I care in the least that my “dutch baby” pancakes have a longer duration than we had thought? Does the data provide scientific cause and effect. Meaning X food always has the identical duration, effects?

Its academic information… not really functional dont you think… ???

As for high/low prevention, how does that work exactly …when as others say the readings a CGM generates is NOT "real time: the readings have a severe lag compaired to accurate veinous reads??? And if they do raise some type of alarm, again they are ACCURATE enough to treat from or they are not.

I cannot wrap my head around the accuracy paradox.

They sound like a technologic ~middle man~ to me (: z

Wait wait wait… the “alarm” those readings are potentially 30 minutes behind the actual BG readings…?
A little too late to let us know after “the bomb” hits… no 8 O ?

I’ll do my best to address each of your points:

As you don’t use a pump, some of the things that I use to fine tune by BG control don’t apply to you. For example, I know (from having a CGM) that pizza take several hours to affect my BG. Because of this, I take a “combo” bolus, which spreads my bolus delivery over several hours. It’s a wonderful tool that the CGM has helped me to use more effectively.

With respect to high/low alarms, I’ve found that the CGM is only five or so minutes behind. Because of this, I’ve set the alarms to sound if the CGM indicates a reading above 180 mg/dl or below 70 mg/dl. This gives me enough time to test (to determine my actual reading) and bolus if high / treat if low. In addition, the DexCom will sound an alarm if I’m raising or falling faster than 3 mg/dl per minute. It’s a great way to predict what will happen in the coming minutes.

Finally, the CGM has saved me far too many times to count. I have severe hypoglycemic unawareness, so I don’t usually feel a low until I’m in the 30s. Without the DexCom, I’d have needed medical intervention at least twice last week alone. You can read my blog for more details on that.

Everyone agrees that the technology isn’t perfect. But, until there is a true “real-time” CGM, this is the next best thing. I haven’t gone without a CGM sensor in a long time; it helps me sleep better at night.

See my response above.

IOB is what again ???

Insulin On Board.

Intellectually I understand CGM’s gives us all kinds of insane data piles to crunch and figure out. Just over 2000 readings in a single week, correct?

Patterns sure, but w/ strips don’t we already have what we really need? Its cute I can tell ten minutes later oooops still dropping, but am not allowed to treat using that information until I reconfirm it, if I understand correctly?

What good does a CGM do us after few months using it? After 288 readings per day the patterns should be fairly obvious after maybe 3-4 months, dont they??? In effect CGM’s are an early warning system…

Hummmngh, much to think about

Well, Yes, in a whole lot of ways. My D changes from day to day, my LIFE changes from day to day- I have a hard time knowing exactly what I’ll be doing at any given moment-The CGMS helps me have a bit of vision into how my body is dealing with the different challenges I’m throwing it. I suppose, if I were an extremely regimented person, I may find a CGMS less useful. But with my FT career, home with 2 teen daughters who NEVER stop moving, and a crazy extended family that specializes in unplanned events, the CGMS is proving it’s worth to me every day.

Have you ever eaten dinner, KNOWN that in the past, you’ve known how much insulin to take for it, went to bed in your sleep range, then woken up the next morning with a 250+ reading? Where did that come from? I don’t need to deal with that anymore, the CGMS will beep at me when I’m rising quickly or over my high limit of 240. At 2:00 am last night, it let me know I was elevated, and still heading higher, and I was able to correct it before it went even further. When I woke this morning, my BG was 89. I didn’t need to set 2 alarms to do middle of the night finger sticks to achieve that-and I believe actions like that will result in a better Ha1c for me, and eventually to a smoother overall glucose trend, with less spikes.

Maybe some people find it too much info, or not useful, but I am slightly addicted to the information at this point. And I think it reassures my husband as well.

I totally agree, Jacky. Once you learn how to use the information CGMS gives you, it is invaluable.

New bG meters are now being held to accuracy/reliability standards which none of the CGMS machines can meet, so the FDA and EU Approvals required that CGMS devices not “pretend” to be as accurate. They would not have been approved without the official usage requiring that non-euglycemic readings be confirmed before proceeding to treatment.

Many people, however, seem to be treating their CGMS devices as a reliable indicator, at least some of the time. This is strictly “off-label” usage by the lazy… including me, on those days when I’ve verified it’s readings to be “spot on”. (Which is nearly every day after the first day, until it becomes inaccurate and I replace it about two weeks later.) Even though lots of us take action directly from CGMS readings, none of us can actually RECOMMEND it for anyone else. It’s a bad habit, and at least somewhat dangerous.

For me, using Dexcom 7+, the “delay” in CGMS readings during falling bG is nearly non-existent. (5-10 minutes.) But I nearly always see a much longer delay during rising bG.

Several of your posts seem to be focusing on “the number” (it’s precision, and promptness, and so on). But in practice, nearly all of us actual users find the trends and alarms to be the key benefit: When you see the shape of the curve change, heading towards a direction you didn’t expect, you really can treat most of your “emergencies” before they have actually occurred.

The greatest benefit in using CGMS (when you’re conscious) is seeing the trend, rather than just a few numbers. Unless you’re poking at least 8x per hour, you can’t really see the shape of the glucose curve change. You can only see a couple of points and try to fit a slope, with no idea whether it’s “steepness” is accelerating or leveling off. And of course, another huge benefit when you’re sleeping, or distracted by work and daily life, is the alarms.

Regular bG meters provide neither of these things.

Hello Rickst29:

First, I appreciate your patience (and time) responding to my original question(s)…

These fuandamental problems must be eliminated before the technology has “validity”. The innacuracy or the potential for it mean whatever the number/trends if we cannot trust the exact reading, then how is the trend.alarm any more accurate? That is fruit from the poisoned tree…

I apologize for the directness of my doubts, but until eliminated I can’t get around the nature of the product. Cute marketing, pretty packaging, but suspect. Regardless when YOU find the slopes, shapes, trends, what value does it hold for you? I know the generic effect pizza or the spin class will have on my numbers. I do not find importance on tracking either one.

Different question though. How long will you wear one, get such patterns, trends before the knowledge generated is superflous to you? Is this something worn fro the rest of your life forward?
Is the technology any more than an “emotional sedative” ??? Truthfully…?

I intend no offense, but have grave concerns with the technology, which in truth I don’t think I understand well. I hope my diabetic peers will suffer my concerns, doubt, to help me perceive differently…

With all due respect, Stuart, I have responded several times to your questions with fact-based, helpful information. All of which clearly demonstrates why I find the CGM to be a valuable tool in my diabetes management. I have provided links to studies, anecdotal evidence, and real-life scenarios. Others have shared their stories, as well, but you seem to want to dislike the technology. I don’t understand why, nor do I understand why you continue to restate your concerns again and again. Especially since each one has been addressed multiple times.

So, for one last time, I can emphatically state that my DexCom wasn’t acting as an “emotional sedative” when it alerted me to the fact that my BG was dropping at dangerously fast rates. I have no trouble stating that since using a CGM, I’ve managed to lower my A1c by 26%. Without a CGM, I have no way of knowing if my BG is low - I just don’t experience any hypo symptoms. This allows me to bolus more aggressively than I would otherwise. I avoid highs far more often than I used to because I’m not afraid of lows like I used to be.

Yes, the technology isn’t perfect. It’s not completely in tune with my meter 100% of the time. But, it’s close enough that it’s a very useful supplement to my 10+ finger sticks per day. Managing my diabetes to the best of my ability is my only motivation. Even if using a CGM only helps me once, that’s one more time than I would have had without it.

I’m a relatively new user of DexCom CGMS, but I’ve also used CGMS in the past with the Medtronic system. I find the DexCom invaluable and I wouldn’t be without it now. If it’s maybe difficult to get your head around the advantages, one of them was very much highlighted for me today. Having had a really bad period of control owing to a stomach virus, I decided to run hourly checks on my blood glucose using my normal meter - I did this for most of the day and recorded the results. I then looked at a graph of my sensor results (every time I’d checked my BG I’d also checked that the sensor was reasonably close, which it was). The sensor graph showed one very low swing and one very high swing, neither of which had shown up at all on my BG results, as the swings had happened between the hourly BG checks. And of course we don’t normally run hourly BG tests do we, so a lot of useful information must get missed if you don’t have CGMS.

It’s an amazing bit of kit. Like Shannon, I’ve used both the Medtronic system and the DexCom. I much prefer the DexCom.


Hello Etta:

Thank you for taking part, I appreciate it.

Inaccurate, or potentially so… trends would be no more ~accurate~ than a single reading they are very much ~…fruit from the “poisoned tree”…~

But why are they invaluable??? They sound like they could be a bad emotional crutch… falsely soothe diabetic fears that are perfectly reasonable to have!?



I am 100% with you. I go as far as saying that I don’t want to imagine life without CGM.


For some people a CGM is a silver bullet and has helped them to drastically improve their bg control. I am one of them. Maybe I could understand your negativity if you had a bad experience with a CGM. This does not seem to be the case. You argue from a theoretical standpoint that CGMs cannot be useful while ignoring the feedback of people who actually use CGMs every day and know a ton more about CGMs than you do. All you might be able to achieve is to discourage people who could benefit from a CGM from going for their own experience. There is no way you can get successful CGM users to abandon their CGM. You would need to pry my CGM off my dead body.