I created a topic way back regarding a study on accuracy, so not my personal results, but reposted here for ease of access:
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.
Study is here: https://care.diabetesjournals.org/content/43/9/e111
Personally, my Dexcom result is higher than my HbA1c result, but both are within the range of good control, but I tend to trust the CGM the most.