The Most Accurate Continuous Monitor

David Mendosa Health Guide June 01, 2008
  • For years many people that I know have been waiting to use Abbott's FreeStyle Navigator continuous glucose monitor. As long ago as February 2005 I wrote in Diabetes Health magazine that, "The FreeStyle Navigator Continuous Glucose Monitor is coming."

    Preliminary studies had indicated that it might raise the accuracy bar. And now, according to a study to be published in this month's issue of Diabetes Care it really will be more accurate than the competition. The Navigator will be more accurate where it counts than the three other monitors that the study evaluated.

    Full disclosure: I have tested and written about one of these monitors, the Guardian REAL-Time, here. I also own 150 shares of a company, DexCom, that makes another. I unwisely purchased
    150 shares of DexCom at $14.832 on January 18, 2006. It's now selling for $7.89 per share. So, if I had a conflict of interest, I certainly wouldn't be writing this article.


    The accuracy comparison included a fourth continuous monitor, A. Menarini's
    Glucoday S. While this Italian monitor is available in Europe, the Food and Drug Administration has not approved it for sale in the United States.

    The comparison, however, did not reach as far as Israel where OrSense
    offers its NBM-200G continuous non-invasive monitoring system. The omission is strange enough that I wrote the lead author.

    The lead author of the new study, Boris
    Kovatchev, PhD, of the University of Virginia, replied today that their "goal was not to make a comprehensive review of all available continuous glucose monitors." Dr. Kovatchev is one of the biggest names in academic testing of our blood glucose monitors. It was Dr. Kovatchev who developed the new low, high, and combined blood glucose indices incorporated into the Accu-Chek Smart Pix Device Reader that I wrote about here last year.

    Another author, William Clarke, MD, also of the University of Virginia is famous for having developed the Clarke Error Grid, which most people use to evaluate meter accuracy. So when two big names in meter testing team up, it's important to sit up and listen. I did, even if the company that I own stock in did worse in accuracy where it counts.

    Where it counts is in hypoglycemia. When our blood glucose levels go too low -- what we familiarly call "hypos" -- getting the correct amount of insulin into our system becomes even more crucial. One study of 14 adults with type 1 diabetes and another of 20, showed that the numerical accuracy of DexCom's original three-day STS monitor was about 30 percent less in both the hypo and normal ranges. They did not test the newer DexCom Seven, acknowledging that, "Recent data collected with the new 7-day DexCom sensor showed improved accuracy of the device..."

    The study concluded that numerical accuracy of Guardian, Navigator, and Glucoday was comparable, "With an advantage to the Navigator in hypoglycemia." The clinical accuracy of the four sensors was similar in euglycemia (the technical term for normal levels). In the hypoglycemic range the Navigator and Glucoday were better.


  • The FDA approved the Navigator for sale early this year, several years after Abbott's original submission. The Abbott press release issued in March says that it "
    will be available in the second quarter of 2008." If your doctor prescribes it, this means that you can get one this month -- assuming that Abbott is a lot quicker to get the Navigator to market than the FDA was to approve it.