Correlation of HbA1c and Continuous Glucose Monitor Time in Range

Background: Current literature is limited to describing the correlation of continuous glucose monitor (CGM) use and improved HbA1cs in patients with type 2 diabetes. There is a lack of literature correlating HbA1c and time in range (TIR). In addition, data such as time spent with low or very low blood glucose levels are not assessed in existing literature. Objective: To assess the correlation between reduction of HbA1c and increase in TIR for patients using CGMs meeting with an interdisciplinary team. Methods: This retrospective chart review includes adult patients seen in an interdisciplinary internal medicine clinic consisting of a pharmacist and nurse practitioner. Data collection included patients with diabetes using CGMs for at least 3 months, who had a visit with the team in the last 12 months. Information collected included demographics, insurance, comorbidities, diabetes medications, HbA1c and CGM data at baseline and 3-month visit, and number of pharmacist medication interventions. Fisher's exact, chi-square, and Mann-Whitney U tests were used where appropriate. Results: HbA1c decreased from 8.6% to 7.5% 3 months later (P = 0.002). The average increase in TIR was 55.5% to 65.1% (P = 0.007). The overall decrease in HbA1c and increase in TIR had a high inverse correlation at baseline and 3 months (r = -0.7 and r = -0.7, P < 0.001). Conclusion: There is a strong inverse relationship between HbA1c and TIR, reduction in glucose variability with a slightly higher incidence time in low/very low following intervention. The type and frequency of pharmacist-initiated interventions support the clinical decision-making potential for pharmacotherapy adjustments.