Living With T1D/October 28, 2026/3 min read

How Accurate Is Your CGM's HbA1c Estimate? New Research Compares Three Major Sensors

A new study tested whether glucose management indicators (GMI)—estimates of HbA1c based on continuous glucose monitor data—match actual lab results across Dexcom, MiniMed, and Abbott sensors. The findings show all three perform similarly, with small differences that don't significantly affect clinical decisions.

PubMed indexed literature

Evidence label explains the kind of source behind this article (for example peer-reviewed literature vs community video). It is not medical advice.

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Key takeaways

All three major CGM sensors (Dexcom, MiniMed, and Abbott) produce GMI estimates that track closely with lab-measured HbA1c values.
While some statistical differences exist between sensors, the variations are too small to matter clinically in most cases.
An updated GMI formula (uGMI) performed similarly to the original formula across all sensor types.
GMI differences ranged from about 0.41% to 0.52% on average—roughly the accuracy you'd expect from this type of estimate.

What Is GMI and Why Does It Matter?

If you use a continuous glucose monitor, you've probably seen your device estimate your HbA1c—the average blood sugar level over the past few months. This estimate is called the glucose management indicator, or GMI. Unlike a lab HbA1c test, which requires a blood draw, GMI calculates this number directly from your CGM data, giving you feedback between clinic visits.

The question researchers wanted to answer: How well does this CGM estimate actually match your real HbA1c lab result? And does it matter which CGM brand you use?

The Study: Comparing Three Sensors Against Real HbA1c Results

Researchers looked at real-world data from adults with Type 1 diabetes using automated insulin delivery (like a closed-loop system) who wore one of three CGM sensors: Dexcom, MiniMed, or Abbott. Over a three-month period, they compared each person's GMI reading with their actual lab-measured HbA1c.

The study also tested whether a newer version of the GMI formula (called uGMI) performed better than the original one. Researchers analyzed data from 383 people over a 90-day window and 375 people over a 28-day window before HbA1c testing.

The Results: Sensors Perform Similarly, Differences Are Small

Across all three sensors, GMI estimates came very close to actual lab HbA1c values. With Dexcom, GMI ran slightly high by about 0.17%. With MiniMed, it ran slightly low by about 0.15%. With Abbott, it was nearly spot-on, off by only 0.08%. These differences were measurable but small enough that they wouldn't change your treatment plan.

The updated GMI formula (uGMI) performed similarly to the original, with comparable accuracy across all three sensors. On average, all estimates were off by roughly 0.41% to 0.52%—a level of precision consistent with how well CGM-based estimates are expected to perform.

Importantly, the accuracy didn't differ significantly between sensor brands, meaning your CGM choice alone won't determine how reliable your GMI estimate is.

What This Means for Your Diabetes Management

If you check your GMI on your CGM device, know that it's a useful trend indicator between lab tests. It gives you real-time insight into how your glucose management is going. However, these results show that GMI estimates and lab HbA1c values can differ by less than 1%, which is normal and expected.

Whether you use Dexcom, MiniMed, or Abbott, your device's GMI estimate performs reliably. The small variations across brands don't suggest one is significantly better than another from this perspective. As always, your actual lab HbA1c remains the gold standard for assessing long-term blood sugar control, especially for clinical decisions. But your GMI is a legitimate tool for tracking your progress day-to-day.

Evidence label

Source: Diabetes, obesity & metabolism. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.

Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.

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