Early CGMs Results in Better 5-Year Glucose Control in Type 1 Diabetes

Children and adolescents with type 1 diabetes (T1D) who begin continuous glucose monitoring (CGM) within the first month of diagnosis maintain more favorable blood glucose control 5 years later than those who start later or never adopt the technology, according to a retrospective cohort study of Korean pediatric patients.¹

Researchers at Seoul National University Bundang Hospital in Seongnam, South Korea, analyzed 216 patients diagnosed with T1D at 18 years of age or younger between January 1, 2015, and September 30, 2024, tracking glycated hemoglobin A_1C (HbA_1C) trajectories for as long as 60 months according to when each patient started using CGM.¹

The findings show that although patients who started CGM earliest had the highest HbA_1C at diagnosis, their glucose control converged with other groups within a year and then pulled ahead over the long term—and patients who never used CGM were the only group to show a sustained, statistically significant rise in HbA_1C during the maintenance phase of the study.¹

Study Design and Population

Investigators classified patients into 4 mutually exclusive groups based on the timing of CGM initiation relative to T1D diagnosis: fewer than 1 month (fewer than 30 days), 1 to fewer than 12 months (30 to fewer than 365 days), 12 months or more, or no CGM use during the 60-month observation period. HbA_1C was aggregated at prespecified intervals—every 3 months during the first year and every 6 months thereafter—and adjusted trajectories were estimated using linear mixed-effects models that accounted for repeated measurements within patients as well as age at diagnosis, sex, and calendar year of diagnosis.¹

Among the 216 patients, 88 (40.7%) started CGM within 1 month of diagnosis, 25 (11.6%) started between 1 and fewer than 12 months, 38 (17.6%) started at 12 months or later, and 65 (30.1%) never used CGM. Mean follow-up was 61.3 ± 34.8 months.¹

Of the 151 patients who ever used CGM, 82.2% predominantly wore real-time CGM (rtCGM) rather than intermittently scanned CGM (isCGM). The proportion of patients who never used CGM fell sharply over the study period, from 41.9% among those diagnosed before 2019 to 8.0% among those diagnosed between 2022 and 2024, tracking South Korea's expansion of CGM insurance coverage.¹

Baseline HbA_1C was higher in the early-CGM group (fewer than 12 months) than in the delayed/no-CGM group (12 months or more, or no use)—12.5% (interquartile range [IQR], 11.0-13.9) versus 11.1% (IQR, 8.8-13.2), respectively (P < .001)—but the gap closed within the first 12 months.¹

A total of 31 additional patients who discontinued CGM for 12 or more consecutive months after starting were excluded from the timing analysis to focus on sustained patterns of use. Those excluded patients were older at diagnosis (mean, 14.4 vs 11.0 years; P < .001) and more often male (67.7% vs 47.2%; P = .052) than patients retained in the analysis, though baseline HbA_1C was similar between the 2 groups (11.6% vs 11.7%; P = .82).¹

Hemoglobin Trajectories Diverge Over Time

All 4 groups showed a steep decline in HbA_1C during the first 3 to 6 months after diagnosis, converging near the target range. Differences became more pronounced after 12 months. Median HbA_1C at 60 months was 6.8% in both the fewer-than-1-month and 1-to-fewer-than-12-month groups compared with 7.7% in the 12-months-or-later group and 7.3% in the no-CGM group (P = .027).¹

When investigators combined patients into early-CGM (fewer than 12 months) and delayed/no-CGM (12 months or more, or no use) categories, no individual time-point comparison between 3 and 42 months reached statistical significance. From 48 months onward, however, median HbA_1C was consistently lower in the early-CGM group, reaching 6.8% versus 7.5% at 60 months (P = .005), and across all post-baseline measurements combined, median HbA_1C was 6.7% (IQR, 6.1-7.6) in the early-CGM group versus 7.1% (IQR, 5.9-9.1) in the delayed/no-CGM group (P = .034).¹

In adjusted mixed-effects models, the no-CGM group reached its lowest estimated mean HbA_1C at 6 months (5.9%; 95% CI, 5.5-6.4) before rising progressively to 7.6% (95% CI, 7.1-8.2) at 48 months. During the maintenance phase of the study, from 12 to 60 months, only the no-CGM group showed a significantly rising HbA_1C trajectory, increasing at a rate of 0.27 percentage points per year (95% CI, 0.16-0.39; P < .001).¹

The fewer-than-1-month and 1-to-fewer-than-12-month groups remained stable over the same period (+0.06 and +0.03 percentage points per year, respectively; both P > .2), and the 12-months-or-later group declined modestly from an elevated baseline (-0.16 percentage points per year; P = .07).¹

The proportion of patients achieving the target HbA_1C of less than 7.0% also diverged by group. The fewer-than-1-month group sustained the highest achievement throughout follow-up (62.2%-81.0%), and the 12-months-or-later group remained lowest beyond 9 months (20.8%-38.5%).¹

The no-CGM group achieved the highest rates during the first year before its performance declined to 47.1% at 60 months. In a sensitivity analysis that modeled CGM status as a time-updated exposure rather than a fixed group assignment, active CGM use was independently associated with lower HbA_1C (-0.40%; 95% CI, -0.67 to -0.12; P = .004), and each additional year of cumulative CGM use was associated with a further reduction (-0.24%; 95% CI, -0.31 to -0.16; P < .001).¹

Mechanisms and Policy Context

The study authors offered several possible explanations for the advantage seen with very early CGM initiation. Introducing CGM soon after diagnosis, when insulin requirements are transiently declining, may support earlier pattern-based insulin titration, reduce therapeutic inertia, and encourage CGM-centered self-management behaviors at a time when families are already highly engaged with diabetes education. Continuous trend and alarm data may also ease fear of hypoglycemia, allowing patients to pursue more ambitious glycemic targets, including the recently recommended HbA_1C goal of 6.5% or lower.¹

The authors cautioned that the retrospective, single-center design cannot establish causation, noting that patients who opt for very early CGM adoption may differ from others in motivation, health literacy, socioeconomic status, and engagement with care. In an exploratory mediation analysis, they found that diagnosis during South Korea's CGM reimbursement era—the country's national health insurance has covered 70% of the cost of CGM consumables for T1D since January 2019, with coverage for patients younger than 19 years expanded to 90% in February 2024—was associated with lower maintenance-phase HbA1c overall (total effect, -1.12%; 95% CI, -1.62 to -0.64).¹

Early CGM initiation accounted for only a modest share of that association, about 17% (indirect effect, -0.19%; 95% CI, -0.40 to 0.00), with most of the benefit attributed to concurrent changes in care delivery, including a national home-based care program launched in January 2020 that pairs newly diagnosed patients with a multidisciplinary team for structured education and remote CGM review; under that program, most newly diagnosed patients at the study center now start CGM within their first week. The study's corresponding author reported receiving honoraria from Abbott, Dexcom, and Medtronic; the research received no external funding.¹

What This Means for Pharmacists

The Korean findings echo a broader body of evidence that timing matters in CGM adoption. A separate retrospective study of 396 patients with T1D of all ages found that early CGM initiation, regardless of insulin delivery method, was associated with lower HbA1c that was maintained up to 7 years after implementation (7.6% vs 9.8%; P < .001), after adjustment for age at diagnosis, sex, and insulin delivery method.²

CGM use overall has also been shown to improve glycemic control in randomized trials. In the DIAMOND trial, 158 adults with T1D on multiple daily insulin injections and baseline HbA_1C of 7.5% to 9.9% who added CGM saw HbA_1C fall 1.1 percentage points at 12 weeks and 1.0 percentage point at 24 weeks, compared with 0.5 and 0.4 percentage points, respectively, in a usual-care group (P < .001). The American Diabetes Association's (ADA) 2023 Standards of Care recommends that rtCGM or a CGM be offered to youth and adults with type 1 or type 2 diabetes on intensive insulin therapy or continuous subcutaneous insulin infusion who are able to use the devices safely.²

Access remains uneven, however. The ADA has stated that "poorer, older Black and Brown Americans and Americans on Medicaid have less access to CGMs than their counterparts," even though people with diabetes are more than twice as likely as those without the disease to receive care through Medicaid. The organization has said that "people with diabetes have the right to access the latest technologies" and is working to address Medicaid coverage barriers to diabetes technology.³

Pharmacists have an established role in helping close that gap and in supporting patients once devices are in place. A scoping review of 20 studies on pharmacist-involved CGM services found that HbA_1C reductions associated with CGM-integrated pharmacist diabetes services ranged from 0.4 to 2.9 percentage points, compared with reductions of 0.5 to 0.8 percentage points in CGM-integrated care that did not involve pharmacists.⁴

The review's authors wrote that "although CGM integration has demonstrated positive effects on pharmacist-involved diabetes care, evidence related to humanistic and economic outcomes is limited, highlighting the need for further research in these areas." The American Pharmacists Association offers a CGM Practice Implementation Toolkit designed to help pharmacists and pharmacy personnel launch and sustain CGM services, covering business planning, reimbursement, workflow design, collaborative practice agreements, clinical resources, and patient-facing marketing materials.⁵

For pharmacists working with pediatric patients and families navigating a new T1D diagnosis, the Korean study's central message is one of timing: initiating CGM as early as feasible, potentially within the first month, rather than waiting for glycemic deterioration to justify the technology, may translate into more favorable glucose control years down the line. The study authors called for prospective, multicenter studies to confirm the causal impact and cost-effectiveness of very early CGM initiation in pediatric T1D care.¹

REFERENCES

1. HHa DJ, Kim HY, Kim J. Timing of continuous glucose monitoring initiation and long-term glycemic trajectories in pediatric type 1 diabetes. Ann Pediatr Endocrinol Metab. Published online September 3, 2026. doi:10.6065/apem.2652270.135

2. Friedman JG, Cardona Matos Z, Szmuilowicz ED, Aleppo G. Use of Continuous Glucose Monitors to Manage Type 1 Diabetes Mellitus: Progress, Challenges, and Recommendations. Pharmgenomics Pers Med. 2023;16:263-276. Published 2023 Mar 31. doi:10.2147/PGPM.S374663

3. American Diabetes Association. Continuous glucose monitors (CGM). Diabetes.org. Accessed September 8, 2026. https://diabetes.org/advocacy/cgm-continuous-glucose-monitors

4. Lee JY, Chan D, Samra M, Tan M, Nguyen J. The impact of continuous glucose monitoring in pharmacist-supported diabetes care: Evidence mapping through a scoping review. J Am Pharm Assoc (2003). 2026;66(3):103034. doi:10.1016/j.japh.2026.103034

5. American Pharmacists Association. CGM: Continuous Glucose Monitoring practice implementation. Pharmacist.com. Accessed September 8, 2026. https://www.pharmacist.com/Practice/Practice-Implementation/CGM