Glucose management indicator, time in range can be valuable tools in diabetes care
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Using the glucose management indicator, continuous glucose monitoring and time in range can improve glycemic control and health outcomes for people with diabetes, according to a speaker at the Cardiometabolic Health Congress.
Grazia Aleppo, MD, professor of endocrinology at the Northwestern University Feinberg School of Medicine, said glucose management indicator can be a good complement to HbA1c in measuring glycemic control and time in range may be used as a predictor for diabetes complications.
“HbA1c is not the only thing out there to understand glucose status,” Aleppo said during the presentation. “You can use glucose management indicator. You can still use HbA1c, but you have to be careful when you use HbA1c in patients who are more advanced with comorbidities, such as kidney disease.”
Glucose management indicator vs. HbA1c
HbA1c has been the gold standard for measuring diabetes-related complications since the Diabetes Control and Complications Trial (DCCT) was completed. However, HbA1c is not a perfect metric because it can fluctuate in response to erythropoiesis, hemoglobin modification, glycation, erythrocyte disruption and analytical interferences, Aleppo said.
Each HbA1c level has a wide range of estimated average glucose. According to data published in Diabetes Care, an HbA1c of 7% has an estimated average glucose range of 123 mg/dL to 185 mg/dL. This overlaps with an HbA1c of 6%, which has an average glucose range of 100 mg/dL to 152 mg/dL, and an HbA1c of 8%, which has an average glucose of 147 mg/dL to 217 mg/dL.
Some of the variability between mean glucose and HbA1c levels can be attributed to the glycation gap, which is the difference between HbA1c and HbA1c predicted by serum fructosamine.
“There are genetic differences that account for this glycation gap, and also many HbA1c plus glucose discordance are present in racial differences,” Aleppo said.
Aleppo recommended providers use glucose management indicator as a complement to HbA1c when adjusting therapy. Glucose management indicator is a CGM-estimated HbA1c based on a formula derived from the regression line of mean glucose concentration points and HbA1c values. Data from 14 to 30 days can be used to calculate glucose management indicator. The greatest correlation between HbA1c, glucose management indicator and mean glucose is for glucose between 144 mg/dL and 160 mg/dL.
“There is always going to be a bit of discrepancy, it is between 0.2% and 0.6%, depending on the levels,” Aleppo said. “The good thing is the discrepancy remains the same over time. Then we can see if, for example, the [glucose management indicator] is higher and the HbA1c is lower, we need to do something to make your glucose level go down.”
Predicting complications with time in range
CGM data are effective for measuring glycemic control in type 2 diabetes as well as type 1. In the Diamond 2 and Mobile studies, people with type 2 diabetes had greater reductions in HbA1c when using CGM compared with self-monitoring blood glucose. In Mobile, participants had a 16% increase in time in range and a 15% decrease in time above range while using CGM compared with before initiating CGM (P < .001 for both).
Time in range is becoming an important metric for predicting complications, according to Aleppo. In DCCT, each 10% lower HbA1c was associated with a 44% reduction of risk for retinopathy. When correlated with time in range, each 10% increase in time in range was associated with a 64% reduced risk for retinopathy.
Similar findings have been reported with carotid intima-media thickness and lower extremity arterial disease, with increases in time in range associated with lower risks for both in type 2 diabetes. Lower time in range is also associated with increased risks for all-cause mortality (HR = 1.08; 95% CI, 1.05-1.12) and cardiovascular mortality (HR = 1.05; 95% CI, 1-1.11) in type 2 diabetes, according to a study published in Diabetes Care.
“Time in range has become an emerging and really good outcome metric for use in clinical trials and clinical practice,” Aleppo said.
References:
- Beck RW, et al. Ann Intern Med. 2017;doi:10.7326/M16-2855.
- Lu J, et al. Diabetes Care. 2021;doi:10.2337/dc20-1862.
- Martens T, et al. JAMA. 2021;doi:10.1001/jama.2021.7444.
- Nathan DM, et al. Diabetes Care. 2008;doi:10.2337/dc08-0545.
- The Diabetes Control and Complications Research Group. Kidney Int. 1995;doi:10.1038/ki.1995.236.
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Aleppo G. Session III: Diabetes. Presented at: Cardiometabolic Health Congress; Oct. 14-17, 2021; National Harbor, Md. (hybrid meeting).
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