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Short Summary
Main recommendation: Rely on the average glucose reading from a CGM (continuous glucose monitor) rather than the A1C-based numbers the app reports or a lab HbA1c, because the CGM average is a direct measurement of the same thing HbA1c tries to estimate. The speaker, Dr. Ben Bikman, says the app's GMI and A1C equivalent are algorithmically or mathematically derived and can differ widely from lab results. He suggests noting the difference but not trusting the derived A1C value.
Key Points
- The speaker is answering a question from a clinician, "Lindsay," who says her patients' CGM apps show a GMI, an A1C equivalent, and a 90-day average glucose that often disagree with each other and with lab HbA1c results.
- The app's A1C equivalent is described as a derived estimate, not a direct measurement, which is why the speaker would not rely on it.
- HbA1c is meant to estimate average glucose over a period of time, so a CGM's average glucose already provides that information.
- A lab HbA1c is not needed to get a useful average, since the CGM can supply it directly.
Details Worth Noting
- Concrete instructions:
- Treat the A1C value shown by the CGM app as a derived number and do not base decisions on it.
- If the lab HbA1c and the app's A1C differ, record the difference as a note rather than trying to reconcile them.
- Use the average glucose reported by the CGM as the primary measure of average glucose over time.
- Obtain the average glucose directly from the CGM when a lab test is not otherwise needed.
- The 90-day average glucose is the app figure the question raised, and the speaker's answer applies to it as the preferred measure, since it comes from the same dynamic pattern the CGM records.
- The transcript does not provide numeric thresholds, specific glucose targets, or information on how the GMI is calculated.
- The speaker's comments are general guidance from a discussion and are not presented as individualized medical advice.
Bottom Line
When a CGM average and a derived A1C disagree, the CGM average is the more direct guide to average glucose, while the derived A1C mainly serves as a note of the discrepancy.
