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Thread: CGMS ISIG and Calibration Guidelines

  1. #11

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    Quote Originally Posted by Darryl View Post
    Monica, do you know a source for any current BG test meter accuracy studies?
    I just found one study about a minute ago from the ADA, comparing four meters. Very Interesting. Has charts.

    http://professional.diabetes.org/Con...004/p439-P.pdf

    I will continue to look for more studies. I want to get a study with the Aviva meter.
    Young adult with type 1 diabetes, autoimmune autonomic neuropathy, and chronic inflammatory demyelinating polyneuropathy (CIDP)

  2. #12
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    Quote Originally Posted by moco89 View Post
    I just found one study about a minute ago from the ADA, comparing four meters. Very Interesting. Has charts.

    http://professional.diabetes.org/Con...004/p439-P.pdf
    The article points out the test strip accuracy degrades with time... I did not know that.
    We have a lot of half-used bottles around for convenience, so maybe that's not a good idea!

    Here is a good study on the base accuracy of the Freestyle vs. the Accucheck. You need to
    register with Medscape but it's a simple and free registration, worth it to get the article:

    http://www.medscape.com/viewarticle/541546_print

    .
    My daughter Leah was dx at age 8. Has used the Omnipod since 2007, Guardian 2007-2013, Dexcom 2007-present and sang the National Anthem at the 2013 JDRF Walk!

    DCCT: The Study That Forever Changed Treatment of Type 1 Diabetes - Improved Glycemic Control in T1 children Using Real-Time CGMS

  3. #13

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    I get some "off readings" with the flash. What's scary is that the cgms I use is more accurate than the flash. In fact, sometimes when I test, the flash is 50 points above the actual cgms reading. I then retest, and the number correlates within one-five points of the cgms reading and will be 50 points lower than the initial fingerstick reading. I have used the flash prior to cgms for a little bit, and I quit using it due to inaccuracy. But now I use the flash for calibration, etc. It's weird that it can be this inconsistent. It's probably the heat, too even though I avoid the heat as much as possible.

    When I get a reading that is off, when I am trying to calibrate, I just mark it as a "control solution" check, and the cgms ignores the inconsistent reading. Plus, the navigator cgms will reject an off reading anyways.
    Last edited by moco89; 07-31-2008 at 11:29 PM.
    Young adult with type 1 diabetes, autoimmune autonomic neuropathy, and chronic inflammatory demyelinating polyneuropathy (CIDP)

  4. #14

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    I understand the Navigator will not allow a calibration if bg is rising or falling. So it's one less issue.

  5. #15

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    Excellent information, thank you very much. I just wonder if my son's BG is always rising or falling and never stable.
    son/27 dx'd 6/06 Pumping Novolog: Omnipod and Dex G4

  6. #16

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    We use the MiniLink for my daughter, and have used it 24/7 for a year and a half now. We get excellent results, generally, our meter readings and sensor readings are within 5 to 10 points of each other. Two week averages are almost always within 5 points. Calibrating correctly is so important.

    I thought it worth noting that if you can't calibrate, don't. You can always put one in later when BG's are stable. Also, when you tell the system that the BG is 120, you will not necessarily see 120 on the screen. It averages the last four or five readings together (and ISIG's) and determines the value.

    One more thing, when you restart (speaking MiniLink here) on day 3, you are starting over with a clean slate. The system does not remember past calibrations. For this reason, if you see a lot of really whacky numbers, you can try to restart the system with a good, stable BG and try again.
    Teresa
    Mom to Katey, age 12, diagnosed 9/05, pumping with Minimed 722 and using CGM
    Mom to Jessica, age 15, non D

  7. #17
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    I learned from one of the MM support techs recently, that it is really important that you only calibrate 3 to 4 time a day and no more. I think when I initially read that in the book I interpreted it as at least 3 to 4 time per day. So, for a long time I'd been calibrating any time we checked BG and Sean's SG readings had been relatively flat over the previous 15 or 20 minutes.

    I'm finding that now that we're only calibrating 3 or 4 times a day, we do indeed get much better results with the CGMS.

    Does anyone here know enough about the algorithm to explain why calibrating more often (but still only when stable) would yield less reliable CGMS readings?
    Steve, Dad to
    Sean age 16 dx 12/27/2006
    Aaron age 15 non-D

    MM Revel 6-6-2011
    MM 523 6-8-11
    MM 522 1-30-08
    MM CGMS 3/27/08
    Guardian (parental monitor) 10/28/2010

    Dexcom G4 3-29-13

  8. #18
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    Quote Originally Posted by stevecu View Post
    I learned from one of the MM support techs recently, that it is really important that you only calibrate 3 to 4 time a day and no more. I think when I initially read that in the book I interpreted it as at least 3 to 4 time per day. So, for a long time I'd been calibrating any time we checked BG and Sean's SG readings had been relatively flat over the previous 15 or 20 minutes.

    I'm finding that now that we're only calibrating 3 or 4 times a day, we do indeed get much better results with the CGMS.

    Does anyone here know enough about the algorithm to explain why calibrating more often (but still only when stable) would yield less reliable CGMS readings?

    It does not matter if you calibrate 3 times or 30 times a day, what's important is how accurate the cal's are.

    It so happens that most people who would calibrate more than 3 times a day are, by necessity, including some BG numbers
    that not appropriate for calibration. These would include BG's outside of the target range, or BG reading taken when BG is
    changing quickly.

    So, it's not that more than 3 cals is a problem, it's that people who cal using every BG reading - rather than being selective -
    are likely inserting some bad cal's into the algoritm.

    The minimum number of cal's I recommend (based on 18 months of successful experience using the MM Guardian) is 3 cals.
    The best time to cal is before breakfast, before dinner (at least 2 hours after the afternoon snack), and at or after bedtime.
    These times are spaced at roughly 8 to 10 hour intervals, at times when BG is typically flat.

    However, any BG not meeting the criteria in my post CGMS Calibration should not be used to cal the CGM.

    However, regardless of when cals are done, 3 good cal's a day are certainly sufficient for reliable and accurate CGM data.
    More cals than that in a day does not hurt (as long as the BG readings are suitable), nor does it help.
    Last edited by Darryl; 09-09-2008 at 09:34 AM.
    My daughter Leah was dx at age 8. Has used the Omnipod since 2007, Guardian 2007-2013, Dexcom 2007-present and sang the National Anthem at the 2013 JDRF Walk!

    DCCT: The Study That Forever Changed Treatment of Type 1 Diabetes - Improved Glycemic Control in T1 children Using Real-Time CGMS

  9. #19
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    Now that makes sense. And combined with your original post, I think provides a logical explanation for our previous "sub-optimal" results. The MM trainer we worked with told us it was okay to calibrate if he was out of range, as long as he was stable.

    What you described is pretty much what weíve been doing the past couple of weeks, I check his BG and calibrate before I wake him up, because heís usually pretty stable at that time of day (and now Iíll also be watching for him to be in range). Iíve told him not to calibrate at school. If heís stable when he gets home Iíll calibrate before his afternoon snack, if not Iíll look for another opportunity before dinner. Then if heís stable at bedtime, Iíll calibrate a third time. If not, Iíll stay up till he is stable and calibrate then.

    I think now Iíll be less reluctant to do additional calibrations as opportunities arise, because sometimes the calibration clock runs out on me (without a stable time to get a BG), and Iím forced to either use a BG that Iíd rather not or stop getting readings.

    Any idea how many prior readings are factored into the algorithm? In other words, how many good calibrations does it take to overcome a bad one?
    Steve, Dad to
    Sean age 16 dx 12/27/2006
    Aaron age 15 non-D

    MM Revel 6-6-2011
    MM 523 6-8-11
    MM 522 1-30-08
    MM CGMS 3/27/08
    Guardian (parental monitor) 10/28/2010

    Dexcom G4 3-29-13

  10. #20
    Join Date
    May 2008
    Location
    Philadelphia
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    4,313

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    Quote Originally Posted by stevecu View Post
    Now that makes sense. And combined with your original post, I think provides a logical explanation for our previous "sub-optimal" results. The MM trainer we worked with told us it was okay to calibrate if he was out of range, as long as he was stable.
    Even if BG is stable, calibrating out of range is not optimal because the CGM's sensor uses an enzymatic reaction
    that is not linear over a wide range of BG. If you have no choice to cal when BG is stable but out of range, it's good
    to cal again as soon as BG is stable and back in-range.
    What you described is pretty much what we’ve been doing the past couple of weeks, I check his BG and calibrate before I wake him up, because he’s usually pretty stable at that time of day (and now I’ll also be watching for him to be in range). I’ve told him not to calibrate at school. If he’s stable when he gets home I’ll calibrate before his afternoon snack, if not I’ll look for another opportunity before dinner. Then if he’s stable at bedtime, I’ll calibrate a third time. If not, I’ll stay up till he is stable and calibrate then.
    Any time you can get an in-range stable BG is a good time to cal. Of course, those times will be different for each
    child, and may even vary depending on the time of year.
    Any idea how many prior readings are factored into the algorithm? In other words, how many good calibrations does it take to overcome a bad one?
    I can't know this for sure... certainly MM keeps it proprietary. However, I've always had great accuracy after any single
    good calibration. Even if prior calibrations are taken into account, accuracy can be restored with one good cal.
    The only time that 2 or 3 cals are usually needed are for a new sensor. This is not because of the cal algorithm, but
    because it can take the sensor 6 to 12 hours to fully stablize from a biological perspective. When you re-start the same
    sensor after 3 days, the sensor is well stabilized and the first good cal will give you good accuracy.
    My daughter Leah was dx at age 8. Has used the Omnipod since 2007, Guardian 2007-2013, Dexcom 2007-present and sang the National Anthem at the 2013 JDRF Walk!

    DCCT: The Study That Forever Changed Treatment of Type 1 Diabetes - Improved Glycemic Control in T1 children Using Real-Time CGMS

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