Association between Flash Glucose Monitors and A1C: A Retrospective Pre-Post Analysis

Background: Randomized controlled trials have investigated the effect of continuous glucose monitors on hemoglobin A1C; however, more evidence is needed to justify their use and expand insurance coverage. Additionally, there are few published studies investigating the A1C lowering effect of flash glucose monitors (FGMs) in broad diabetes populations with varying insulin requirements. This analysis aimed to help fill this gap in medical literature and help clinicians evaluate costs/benefits when considering FGMs for their patients with diabetes. Objectives: To determine the association between FGM use and A1C reduction in patients with type 1 or type 2 diabetes mellitus regardless of insulin dependence. Methods: Pharmacy dispensing records were used to identify patients for inclusion. Patients who received a FGM from a University of Utah pharmacy between July 7, 2018 and July 7, 2020 were included. Patients who did not receive at least an 84-day supply of FGM sensors or did not have a baseline or follow-up A1C were excluded. Baseline and follow-up A1Cs, defined as A1Cs that are within one year before and 3-12 months after the FGM dispense date, were collected for each patient. New diabetes medications within a six-month window of the initial FGM dispense date were also recorded. Outcome variables were collected before and after patients received their first FGM (pre-FGM vs. post-FGM, respectively). The primary outcome was the difference between baseline and follow-up A1C for each patient. Secondary outcomes were the difference in baseline and follow-up A1C for various clinical subgroups within the overall sample. Descriptive statistics were used to summarize baseline characteristics and outcome data. Paired Student’s t-tests were used to evaluate outcome differences (α=0.05). Results: Fifty-seven patients (50.8% male; mean age: 49 years) were included. For the primary outcome, the average baseline and follow-up A1Cs were 9.33% and 8.32%, respectively for a difference of -1.01% ([95%CI -1.31:-0.72]; p<0.0001). Conclusions: The use of FGMs is associated with decreases in A1C within a cohort of patients at one health system. Further effort to determine impact of FGM on clinical and economic outcomes is warranted.