Patterns of One-Year Change in HbA1c and Continuous Glucose Monitoring (CGM) Metrics in Older Adults with Type 2 Diabetes

BACKGROUND: How changes in hemoglobin A1c (HbA1c) and continuous glucose monitoring (CGM) metrics track together over time is poorly understood, particularly in type 2 diabetes. We investigated the patterns of change in HbA1c and CGM metrics among older adults with type 2 diabetes. METHODS: We analyzed data from 88 Atherosclerosis Risk in Communities (ARIC) study participants (baseline age, 82 years; 28% Black race and 42% women) who had HbA1c and 14-days of CGM assessed by standardized protocols at visit 9 (2021-22) and visit 10 (2023). HbA1c, CGM mean glucose, and time in range (TIR, 70-180 mg/dL) were compared across visits. Discordance was defined as having a different direction or magnitude of change, based on an absolute HbA1c change of 0.5% and the corresponding changes in CGM metrics derived from linear mixed-effect models. RESULTS: Over a median of 1.6 (IQR, 1.3-1.8) years, HbA1c, CGM mean glucose, and TIR showed moderate to strong correlations (r ∼0.5 to 0.7) across visits, and HbA1c had the lowest within-person variability (CVw = 8.4%). Approximately one-third of the participants had discordant changes between HbA1c and CGM metrics, with percentage agreement of 68.2% between HbA1c and CGM mean glucose, and 67.0% between HbA1c and TIR. Similar results were found in subgroups by sex, race, diabetes medication use, and after excluding participants with reduced kidney function. CONCLUSIONS: Among older adults with type 2 diabetes, long-term changes in HbA1c and CGM metrics are frequently discordant. This suggests the complementary nature of using HbA1c and CGM together to monitor glucose control.