Using a continuous glucose monitoring (CGM) system for a limited period of time — to look at the amount of time people with diabetes spend in their target glucose range — may be a better way to assess how well diabetes treatments are working than using A1C levels as a guide, according to a recent presentation given at the 2021 Heart in Diabetes conference and reported in a Healio article.
Limitations of A1C
A1C (a measure of long-term blood glucose control) has long been a standard blood test used to assess how well diabetes treatment and management are working, and whether any changes in medications or other treatment protocols are needed. But A1C has some inherent limitations as a measurement. This test looks at the percentage of hemoglobin in the blood (a protein in red blood cells that transports oxygen and carbon dioxide) that has become glycosylated, or stuck to a glucose molecule. The higher a person’s blood glucose levels are over the course of the life of their red blood cells — about two to three months — the higher the percentage of hemoglobin that will undergo this reaction. But it’s conceivable that someone with diabetes whose glucose levels vary wildly between high and low — both of which are harmful — could have the same A1C level as someone with fairly steady, mostly good blood glucose control.
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The fact that A1C tends to approximate a person’s average blood glucose level, rather than look at how their glucose level changes or remains constant over time, makes a CGM assessment an attractive alternative, according to the conference presentation by George Grunberger, MD, chairman of the Grunberger Diabetes Institute in Bloomfield Hills, Michigan. Other problems with A1C include its unreliability in people with certain medical conditions, as well as differences in its correlation with average glucose levels in people from different racial or ethnic backgrounds.
In contrast, CGM can give a far more detailed picture of how a person’s blood glucose levels change over time, as well as their average glucose level. But Grunberger contends that a person’s average glucose level is much less important than the amount of time they spend in their target glucose range — with a common target range being between 70 mg/dl and 180 mg/dl. Minimizing the amount of time spent with hypoglycemia (low blood glucose) is crucially important for any treatment plan, and using CGM for an assessment is a good way to help accomplish this, according to Grunberger — with 10 to 14 days of wearing a CGM system, with about 100 glucose readings per day, needed to get a good sense of how someone’s glucose levels tend to change over time.
There are now at least a couple of studies showing that increased time spent in a target glucose range is linked to fewer long-term diabetes complications. One study from 2018 showed that among hospitalized patients with type 2 diabetes, those who spent at least 86% of their time in range had the lowest incidence of diabetic retinopathy (eye disease). And a 2019 study showed that time in range was linked both to measures of retinopathy and to the amount of protein in someone’s urine (microalbuminuria), which can be a marker of both kidney and heart function. Other data has shown that time in range is also linked to cardiovascular function and peripheral nerve function in people with type 2 diabetes.
What’s more, one projection showed that if time in range for people with type 1 or type 2 diabetes increased from 58% — the current average — to 70% or 80%, the potential cost savings from reduced diabetes complications could range from $6.7 billion to $9.7 billion over 10 years. This means that the extra costs associated with CGM-based assessments could more than pay for themselves over time, if they led to improved diabetes treatment and management.
Want to learn more about A1C? Read “How to Lower A1C Levels Naturally,” “How to Lower Your A1C Levels: More Steps You Can Take” and “HbA1c: What It Is and Why It Matters.”