Two Ways to Measure Blood Sugar Control: What Researchers Found

People with Type 1 diabetes track their blood sugar control using two main measurements. A1C, measured through a blood test at the doctor's office, shows average blood sugar over about three months. GMI—the glucose management indicator—is estimated from continuous glucose monitor (CGM) data and is designed to predict what a person's A1C would be.

GMI has become increasingly popular in research because CGM devices are common and give real-time data. But a recent study raises an important question: do these two measurements always agree?

Researchers analyzed data from three large Type 1 diabetes clinical trials involving children, teenagers, adults, and older adults. They compared A1C and GMI measurements taken at the start and after three months of treatment.

The findings revealed an important pattern: the two measurements don't always change in the same way. While there was some connection between A1C and GMI changes (a modest correlation), the relationship depended on where someone started.

For people beginning with an A1C above 9%—indicating higher blood sugar levels—A1C dropped more than GMI predicted. When A1C was between 7% and 9%, the same pattern appeared but was less dramatic. However, for people who started with an A1C below 7% (well-controlled diabetes), both measurements tracked similarly.

GMI underestimating true improvement is significant because clinical trials use these measurements to judge whether new treatments actually work. If GMI is used as the main way to measure success, researchers might conclude a treatment is less effective than it truly is—especially for people starting with higher blood sugar levels.

This is particularly important for treatments aimed at people whose diabetes is harder to control, since those are the individuals where GMI and A1C showed the biggest differences.

The researchers recommend that clinical trials continue using lab-measured A1C alongside or instead of GMI, particularly when evaluating how well treatments work. This ensures that the true effectiveness of new therapies isn't hidden by measurement differences.

As CGM technology becomes more central to diabetes care and research, understanding how these different measurements relate to each other will help ensure both patients and researchers get an accurate picture of blood sugar control.

Origin: endocrine.org (News report). Evidence: News report, corroborated with 1 indexed study. 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.