Time in range, other CGM metrics linked to diabetic retinopathy risk in type 1 diabetes
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Key takeaways:
- Each 5 percentage point decrease in time in range increased the odds for diabetic retinopathy by 24%
- Higher time above range was also linked to an increase in diabetic retinopathy risk.
Providers can use continuous glucose monitoring metrics as well as HbA1c to assess diabetic retinopathy risk for adults with type 1 diabetes, according to findings published in Diabetes Technology & Therapeutics.
“Our study confirms that time in range, as well as time in tight target range, is associated with incident diabetic retinopathy,” Viral N. Shah, MD, associate professor of medicine and pediatrics in the adult clinic of the Barbara Davis Center for Diabetes at the University of Colorado Anschutz Medical Campus, told Healio. “We only evaluated diabetic retinopathy in our study, but I am confident to extrapolate this finding to other microvascular complications such as nephropathy risk as well.”
Shah and colleagues conducted a single-center longitudinal study with 163 adults aged 18 years and older with type 1 diabetes who had results from an eye examination available from June 2018 to March 2022. Adults were considered to have incident diabetic retinopathy if the condition was found during an eye exam following two consecutive prior exams without diabetic retinopathy. Adults were divided into a group diagnosed with diabetic retinopathy and a control group without diabetic retinopathy. Raw CGM data were collected for up to 90 days at each clinic visit performed after Jan. 1, 2013, and prior to the date of diagnosis for those diagnosed with diabetic retinopathy or the date of the last visit in the study period for the control group. HbA1c were also collected during visits.
There were 71 adults diagnosed with diabetic retinopathy and 92 in the control group without diabetic retinopathy. The control group was older (mean age, 38 years vs. 27 years) and had a longer diabetes duration (mean duration, 20 years vs. 15 years) than the diabetic retinopathy group.
The diabetic retinopathy group had a higher HbA1c, lower time in range with a glucose level of 70 mg/dL to 180 mg/dL and higher time above range with glucose of greater than 180 mg/dL than the control group. Time below range with a glucose level of less than 70 mg/dL and less than 54 mg/dL were higher in the control group vs. the diabetic retinopathy group.
After adjusting for age, diabetic duration and CGM type, each 0.5% increase in HbA1c was associated with increased odds of developing diabetic retinopathy (adjusted OR = 1.24; 95% CI, 1.05-1.48; P = .01). Each 5 percentage point decrease in time in range (aOR = 1.18; 95% CI, 1.03-1.35; P = .02) and time in tight range with glucose between 70 mg/dL and 140 mg/dL (aOR = 1.28; 95% CI, 1.08-1.51; P = .004) were associated with increased odds for diabetic retinopathy.
“We hear this question a lot, which CGM metric is better; time in range or time in tight range,” Shah said. “There is a very good correlation between time in tight range and time in range, and therefore, it is very difficult to analyze and state that time in tight range is better than time in range for diabetic retinopathy risk.”
A higher likelihood for diabetic retinopathy was also observed with each 5 percentage point increase in time above range (aOR = 1.2; 95% CI, 1.06-1.36; P = .005).
Shah said a prospective study with prespecified outcomes and a larger sample size, similar to the design of the Diabetes Control and Complications Trial (DCCT), would be best to further analyze associations between CGM metrics and diabetes complications.
“The main question is around the funding of a new DCCT-like study, it would cost a lot to do DCCT again,” Shah said. “Therefore, we designed this mini DCCT-like study. I hope to see our findings being replicated by others.”
For more information:
Viral N. Shah, MD, can be reached at viral.shah@cuanschutz.edu.
Perspective
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Diana Isaacs, PharmD, BCPS, BCACP, BC-ADM, CDCES, FADCES, FCCP
The recent study by Shah and colleagues demonstrated that higher time in range of 70 mg/dL to 180 mg/dL as well as time in tight range of 70 mg/dL to 140 mg/dL was associated with lower odds of developing diabetic retinopathy.
This study is important as continuous glucose monitoring use is rising quickly, and time in range is often used to assess glycemic management. Although HbA1c has long been the standard of care, its limitations include that it provides only an average and can also be falsely high or low based on various conditions that affect red blood cell turnover. Although CGM metrics are widely used in practice and even endorsed by major organizations like the American Diabetes Association to be used in place of or in addition to HbA1c, we lack outcome data linking time in range to microvascular and macrovascular outcomes.
The findings from this study are important to demonstrate the powerful benefits of optimizing time in range. Just a 5 percentage point increase in time in range was significant, which can be a very achievable and motivational tool for people with diabetes. Strengths of this study include that it was longitudinal using up to 7 years of data as compared to most previous studies in this space which were cross-sectional, and only assessed one point in time. It’s also great that they looked at time in tight range, which is likely a metric we are going to see grow in the coming years as CGM use increases amongst people with type 2 diabetes on non-insulin therapies.
However, there are some limitations. For example, most participants had commercial insurance and were non-Hispanic white people with type 1 diabetes. This was also a retrospective study design as compared to the landmark DCCT trial, which was prospective, although it would be very expensive and time consuming to replicate. Because of the lack of diversity, we can’t extrapolate the results to other populations and further studies should be done with larger more diverse populations, including people with type 2 diabetes, to further validate the relationship between time in range and diabetic retinopathy and other diabetes complications.
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