Nearly 25% of patients served in the US Department of Veterans Affairs (VA) have been diagnosed with type 2 diabetes mellitus (T2DM), although the prevalence among adults in the United States is 9%.1 Patients with DM typically monitor their blood glucose using intermittent fingerstick self-testing. Continuous glucose monitoring (CGM) might offer a more comprehensive picture of glucose control to improve disease management. Within the VA, criteria for CGM use varies among facilities, but generally veterans prescribed at least 3 daily insulin injections and 4 daily blood glucose checks qualify.2
CGM therapy has been extensively researched for type 1 DM (T1DM); however, outcomes of CGM use among older adults with T2DM have not been fully evaluated. In a 2018 review of randomized clinical trials evaluating CGM use, 17 trials examined only patients with T1DM (2009 participants), 4 included only patients with T2DM patients (547 patients), 3 evaluated patients with T1DM or T2DM (655 patients), and 3 included women with gestational diabetes (585 patients).3 Of 27 studies that included change in hemoglobin A1c (HbA1c) as an endpoint, 15 found a statistically significant reduction in HbA1c for the CGM group. Four trials evaluated CGM use in adults with T2DM and 3 found no difference in HbA1c overall. However, 1 study found a difference in HbA1c only in individuals aged < 65 years, and another study found a greater improvement in the CGM group (approximately 0.5%).4,5 These mixed results indicate a need for further subgroup analysis in specific populations to determine the optimal use of CGM in adults with T2DM. Although this study was not designed to measure changes in hypoglycemic episodes or the relative efficacy of different CGM products, it establishes a baseline from which to conduct additional research.
Our primary objective was to determine change in HbA1c in each patient from the year before CGM initiation to the year after. Secondary objectives included changes in blood pressure (BP), weight, and diabetes-related hospital and clinic visits during the same time frame. We also completed subanalysis comparing primary outcomes in engaged or adherent patients compared with the entire study group. This study was completed as a quality improvement project with approval from the Lexington Veterans Affairs Health Care System in Kentucky information security office and was exempted from institutional review board review.
Methods
This project was a retrospective evaluation using the VA database of patient records. Rather than using a control group, our study used a pre–post model to determine the impact of CGM for each patient. For the primary outcome, average HbA1c values were calculated for the year before and year after CGM initiation. Hemoglobin and hematocrit values were included if reported within 3 months of the HbA1c values to ensure validity of HbA1c results. Average HbA1c was 13.37 g/dL (range, 10.5-17.3), and average hematocrit was 43.3% (range, 36-52). Change in average HbA1c was recorded for each patient. Based on research by Taylor and colleagues, a change in HbA1c of 0.8% was considered clinically significant for this project.6
Mean BP and weight were calculated for the years before and after CGM initiation. Only values for routine clinic visits were included; values taken during an acute health incident, inpatient stay, infusion clinic appointments, or home readings were excluded. Changes were recorded for each patient. Patient encounter notes were used to determine the number of DM-related hospital, emergency department, and clinic visits, such as nephrology, podiatry, vascular medicine, or infectious disease clinic or inpatient encounters during the study period. Routine endocrinology or primary care visits were not included, and patient care notes were consulted to ensure that the encounters were related to a DM complication. The change in number of visits was calculated for each patient.
Adherence was defined as patients receiving active medication management, documented treatment regimen adherence, and > 4 annual endocrinology clinic visits. Active medication management was defined as having > 1 dosage or medication change for oral or noninsulin antihyperglycemics, initiation, or adjustment of insulin dosages according to the patient records. Treatment adherence was determined based on medication reconciliation notes and refill request history. Only endocrinology clinic visits at VA outpatient clinics were included.
Study Population
A sample of 166 patients was needed to detect an HbA1c change of 0.8 per power analysis. The normal approximation method using the z statistic was used, with 2-tailed α = 0.05, β = 0.05, E = 0.8, and S = 1.2. We randomly selected 175 patients among all individuals with an active prescription for CGM in 2018 and 2019, who had a diagnosis of T2DM, and were managed by VA endocrinology clinics (including endocrine clinics, diabetes clinics, and patient aligned care team clinics) at 87 VA medical centers. Patients with types of DM other than T2DM were excluded, as well as those with a diagnosed hemoglobinopathy or HbA1c < 10 g/dL. The adherent subgroup included 40 patients of the 175 sample population (Table 1).
Results
Both the total population and the adherent subgroup showed reduction in HbA1c, the primary endpoint. The complete population showed a HbA1c change of –0.3 (95% CI, –0.4 to –0.2), and the adherent subgroup had a change of –1.3 (95% CI, –1.5 to –1.2). The total survey population had a mean change in weight of –1.9 lb (–0.9 kg) (95% CI, –3.7 to –0.1) and the adherent subgroup had an average change of –8.0 lb (–3.6 kg) (95% CI, –12.3 to –3.8). Average systolic BP changes were –0.1 mm Hg (95% CI, –1.6 to 1.5) in the total population and +3.3 mm Hg (95% CI, –0.01 to 6.22) in the adherent subgroup. A decrease in total encounters for DM complications was observed in the population (–0.3 total encounters per patient, 95% CI, –0.5 to –0.2) and the adherent subgroup (–0.6 total encounters per patient, 95% CI, –1.0 to –0.1) (Table 2).