CGM Accuracy Comparison (New Study)

Diabetes Technology
4

Clarifying a bit, since it’s dense…

Term

  • GMI: glucose management indicator estimates A1c from meter readings

Real-Time (rtCGM)

  • CareLink Pro/Personal, Dexcom G5
  • Symmetric variance of GMI around A1c

Intermittent Scanning (iscCGM)

  • FreeStyle Libre
  • Higher GMI compared to actual on 75% of users

Generally

  • About 50% had differences between GMI and A1c of >0.5%
  • Similar patterns were observed regardless of weight or age
  • With average A1C < 7.5, GMI was higher than actual, more often in isCGM
  • With average A1C > 7.5, A1c was higher than GMI, more often in rtCGM
  • With average A1C > 7.5, isCGM was generally accurate

Synopsis

  • If you have good control, you can trust your Dexcom or CareLink, but your Freestyle might be overestimating average A1c.
  • An alternative assessment might turn up that the pattern of scanning by FreeStyle users is different, and they more often scan when they are high, but not when they are low.
  • If you have poor control, the real-time CGM is possibly underestimating your A1c.
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