Meter accuracy, CGMs and how to handle the discrepancy

I´m waiting for my first CGM ever (a Dexcom G4 Platinum).

My question is how to actually benefit from the information I will get from it. I know it´s more of at trend device than anything else, but so is the meters we use.

I am norwegian and the meters allowed for use in my country have an +/- 25% accuracy (I know yours is 20%). In my case this means getting a reading at 6 mmol/l (108 mg/dl) could mean I`m actually anywhere between 4,5 and 7,5 (81-134 mg/dl). This is only a problem if I want to be in tight controll and avoid those over 8-readings (145) and preferably stay in the 5 to 6 range (90-110 mg/dl) before meals and during the night. And I want to be in tight controll.

First question is how you handle the inaccuracy according to your meter.

Second question would be how you handle the added discrepancy of the Dexcom radings. Even though they have improved the sensor it´s still about +/- 20%. And wouldn`t that in fact be on top of the allready where-am-I-actually meter reading?

Oh… and a final question:
Why on earth do we get accurate recommendations from our doctors when accuracy in fact is not obtainable?

Maybe I just answered my own questions reading this?

I would still love to hear how others cope with the frustration, esp. the one choosing between staying a bit high or dosing and getting low when it turned out bls really was fine.

So how do you deal with it?

Ane hints, tips or ticks?

Start with your blood glucose. For example BG=100mg/dL, measured in clinical lab with a ±2% means it was really 98-102mg/dL. For your meter this would be 75-125mg/dL. Remember, if you did several tests, you should get a bell curve distribution. This is the reason the Dexcom 7+ would use two tests for startup. The D 7+ is also watching the change on start up to determine which way BG is going. The biggest help will be to see what is going on in your body. When you do a BG after a meal, is the BG still going up, at the top, or started back down. The other is a hypoglycemic alarm. This is where it is a lifesaver for me.

One rule I always follow: NEVER inject insulin with out a finger stick BG. Also, enter the BG and the insulin dose in the Dexcom unit for log book information to use later.

Thanks for your reply, Jay.

I know the CGMs are just trend devices,- really just like our regular meters in my opinion since we can never know what the blood sugar really is.

If I get an reading of 7 mmol/l after a meal I automatically want to lower my blood sugar and inject some insulin. But also knowing that a 7 mmol/l really could be a 5,6 or an 8,4 makes it difficult to decide whether I should inject som insulin or not. Because if it`s really 5,5 i would just leave it alone and injecting would get me too low no matter what amount I inject. So I guess I wonder what strategies people use to handle this. And I´m also wondering how too handle this with an extra device on your hand giving you more inaccurate numbers to deal with.

I have a Dex 7+ and I find it to be very close to my fingersticks in most cases. And the trends are invaluable. For corrections, I'm conservative, because I can always correct a little more if my BG doesn't drop enough, and I'd rather be a little high than have a low. The other thing is that if I limit my carbs, I am able to get a much tighter range than if I eat a lot of carbs. I'm sorry that's so, but it's the only way I'm really able to get good control. I figure if it's a range, and I stay in it, I'm doing great. Obviously I can't get precise numbers, but if I'm in range, I don't worry about it. And perfect meter or CGM accuracy is not crucial to a range -- doesn't matter if I'm 88 or 128 -- either way, I'm in range. Does that make sense?

Yes it does make a lot of sense, Natalie._c-. Thank you for your reply.

I need new thinking strategies for handling my meter and soon-to-come CGM. I wonder if I correct to much and experience too many lows from that and that it´s not caused by miscalcuations but a meter that´s not correct enough to do such tiny corections. I just have to relax a bit and let my bls fluctuate in a wider range than I do now, hold back on corrections and then check back with a Hba1c-test in a couple of months to see how it´s going.

I have found the G4 to be considerably more accurate (to my meter, anyway) than the 7+ was. I am learning about my trends - which really is helpful. Even though my Dex numbers are often (but not always) dead on with the meter's, I don't take insulin until I check the meter. I also look at both: So, for instance if I am high (>140) but the Dex is indicating that I am coming down - I leave it and re-check in an hour. I only bolus extra insulin if I am really high. Same applies to lows, except if I am really low then I will either lower or pause my pump and/or eat something. It really depends a lot on how I am feeling and what trend the G4 is showing. Hope this helps.

It does help. Thank you for sharing your thoughts. I`m going to start my Dexcom G4 tomorrow.

Good luck with your G4! Your initial posting touches on a "kjepphest" of mine: Why can't the glucose meter manufacturers invest some time and money into improving their accuracy? Plus-minus 20 percent is ridiculously sloppy, and the spokesperson for that industry simply states that "it is accurate enough" or words to that effect. I am hoping that the improved accuracy of the Dex G4 will start a competition on this score. If the CGM systems can improve to around 10 percent accoracy, can the glocumeter manufacturers continue to charge about $1 per test strip and get away with their sloppy approach?
Please keep us posted on your progress with the G4. I have said before that there is a learning curv with CGMs, but it is not a challenging one, and within a few weeks you will be on top of it.
(Incidentally, when I went to Grefsen gymnasium many decades ago I had a classmate named Siri who had Type 1 diabetes. She did not manage it and has long since died.) You are on a better course! Lykke til!