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Diana Isaacs, PharmD, BCPS, BCACP, BC-ADM, CDCES, comments on the accuracy and selection of CGMs in treating diabetes and shares insight on the evolution of CGM systems over the past year.
Diana Isaacs, PharmD, BCPS, BCACP, BC-ADM, CDCES: When we think about CGM [continuous glucose monitor] accuracy, they’ve all shown that they’re pretty accurate. We have a term we use to describe the accuracy: mean absolute relative difference [MARD]. The lower, the better. According to the FDA, when MARD is below 10%, the device is accurate enough to base treatment decisions on. That would include treating hypoglycemia or determining insulin doses based on the numbers. We feel pretty comfortable with their accuracy. It continues to improve.
One thing we have to be aware of is that there’s a slight lag time with CGM. The gap is closing, so the lag time isn’t what it was like 10 years ago. But because fingersticks are measuring the capillary and CGM is measuring interstitial fluid, there’s a slight delay. That means that if somebody recently ate something, the glucose on the fingerstick might be a little higher than it would be on the CGM. Similarly, if someone recently exercised or recently gave an insulin injection, that number may be a little different. Educating people on those differences is very important.
Beyond that, calibration is sometimes a factor that goes into device selection. When you calibrate, you’re essentially doing a fingerstick and entering the result into the device to calibrate it. Any time you do that, you could be entering in some error, because we know fingersticks aren’t perfect. If you have anything sticky or sweet on your fingers, or if you didn’t get a good enough sample, that can skew the reading. If you put a bad reading into the device, you’re probably going to skew the accuracy. That can be a determination. Devices that are factory calibrated are often preferred because you have less interference, and it’s easier for the person because they don’t have to do additional fingersticks.
CGMs have evolved so much over the last several years. It has been amazing. Some big advancements are regarding calibrations. It used to be standard that all CGMs required fingersticks, and now we have factory-calibrated options that don’t require any fingersticks or have them as optional. There have also been impressive advancements with wear time. One of our devices goes up to 14 days. Another is implantable and goes up to 180 days. Wear time has evolved. It used to be about 3 days to start.
The other area where we’ve seen a lot of advancement is with integration. We have CGMs that integrate with insulin pumps to have automated insulin delivery, which is incredible. We also have CGM integration with connected insulin pens, which can also use those data and be able to view it in 1 report, which is remarkable. Several mobile apps can link in with these CGM data. Accuracy has improved a lot over the years, and we’re seeing that the sensor is getting smaller. They used to be much larger, and now you barely notice it and barely feel it. There have been lots of great positive enhancements over the years.
Transcript Edited for Clarity