Your CGM Looks Great, But Your HbA1C Doesn’t: Which Should You Trust?
Original Article: https://www.medscape.com/c99/p10/your-patients-cgm-looks-perfect-their-a1c-doesnt-which-one-2026a1000xg9
The Study
The article examines what doctors should consider when a patient’s continuous glucose monitor (CGM) results look good, but their HbA1C tells a different story. CGMs provide detailed information about glucose levels throughout the day, while HbA1C estimates average blood glucose over roughly the previous 2–3 months. Because these tests measure glucose in different ways, they do not always agree.
Why CGM and A1C Can Differ
A1C measures the amount of glucose attached to hemoglobin in red blood cells. Factors that affect red blood cell lifespan or turnover, such as anemia, certain hemoglobin conditions, kidney disease, blood loss, or recent transfusion, can cause HbA1C to be higher or lower than expected based on a person’s actual glucose levels. Differences can also occur because CGM and HbA1C capture glucose over different time periods.
What Doctors Should Look At
When CGM and HbA1C do not match, healthcare providers should look at the entire glucose picture rather than automatically relying on one measurement. CGM metrics such as time in range, glucose patterns, and the glucose management indicator (GMI) can provide information that HbA1C cannot, including glucose highs, lows, and daily fluctuations. At the same time, HbA1C remains an important measure of longer-term glucose exposure and diabetes complications.
Why It Matters
A mismatch between CGM and HbA1C does not necessarily mean that one test is wrong. Research has found that substantial differences between the two measurements are not uncommon. When the results are consistently and substantially different, guidelines recommend investigating possible reasons for the discrepancy and considering other measures of glucose control when appropriate.
