The HbA1c blood test has long been used to evaluate long-term blood glucose control in people with diabetes. This test gives a snapshot of blood glucose levels over the last 3 to 4 months, indicating how high or low someone’s average glucose levels are. But HbA1c doesn’t tell you anything about another important aspect of blood glucose control: variability.
Highly variable blood glucose levels are considered unhealthy for a number of reasons, including a higher risk for both hyperglycemia (high blood glucose) and hypoglycemia (low blood glucose). Over time, the stress these conditions put on your body can cause lasting damage, in addition to being potentially dangerous in the moment. So it’s best to keep swings in your blood glucose levels to a minimum.
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That’s why the results of a recent study on blood glucose control in youth with type 1 diabetes are concerning. Published in the journal Diabetes Care, the study included 107 participants, ages 8 to 17, with diabetes for at least a year. Each participant wore a continuous glucose monitoring (CGM) system that recorded glucose levels for 4 weeks as part of the study. Most participants, 88%, wore an insulin pump as part of their regular diabetes treatment.
In addition to their CGM tracking, participants all took an HbA1c test as part of the study. The average HbA1c result was 7.8%, indicating somewhat less than ideal — but not terrible — blood glucose control overall. But the real-time glucose data from CGM showed why HbA1c is only one part of the picture when it comes to evaluating blood glucose control.
There was greater variability in CGM glucose readings among participants who hadn’t gone through puberty yet, compared with those who were going through or had already gone through puberty. The average standard deviation — a statistical measure of variability — in the pre-puberty group was 86 mg/dl, compared with 79 mg/dl in the puberty group and 77 mg/dl in the post-puberty group. In other words, the pre-puberty group had glucose readings that were furthest away from their average reading.
One strong predictor of greater glucose variability was the amount of time spent with a reading under 70 mg/dl. That means greater variability wasn’t shown to any significant degree in a higher HbA1c level. In fact, in many cases, a lower HbA1c level could be undesirable if it resulted from greater variability and more time spent under the 70 mg/dl threshold.
The researchers concluded that because of their greater glucose variability, pre-puberty youth with type 1 diabetes could benefit from wearing a CGM system. This could help their health-care providers spot problems with blood glucose control that aren’t revealed by a standard HbA1c test or more occasional fingerstick tests.
Want to learn more about parenting a child with type 1 diabetes? Read “The Type 1 Diabetes Diagnosis,” “Type 1 Diabetes and Sleepovers or Field Trips,” “Writing a Section 504 Plan for Diabetes” and “Top 10 Tips for Better Blood Glucose Control.”
A freelance health writer and editor based in Wisconsin, Phillips has a degree in government from Harvard University. He writes on a variety of topics, but is especially interested in the intersection of health and public policy.