Trajectory of Glycemic Control from Late Adolescence to Young Adulthood with Type 1 Diabetes: A Longitudinal Study

INTRODUCTION: Improving outcomes for transition-aged patients with type 1 diabetes (T1D) requires understanding glycemic trajectories and modifiable factors. We evaluated longitudinal glycated hemoglobin (HbA1c) trends, target attainment, and associated factors in Korean youth with T1D. METHODS: This retrospective cohort included 354 patients diagnosed before age 14 years with HbA1c data at three or more distinct ages between 15 and 22 years, followed at Seoul National University Children's Hospital during 1999-2024. Linear mixed-effects models assessed factors associated with the HbA1c trajectory. RESULTS: Mean HbA1c declined from 9.0% (75 mmol/mol) at the age of 15 years to 8.2% (66 mmol/mol) at the age of 22 years (-0.103% [-1.1 mmol/mol] per year, p < 0.001). Older age, male sex, continuous glucose monitoring (CGM) use, and parental college education were independently associated with lower HbA1c over time (all p < 0.05). At the age of 22 years, there were no CGM users in the 2006-2015 cohort, whereas 25.2% used CGM in the 2016-2024 cohort. At this age, 19.6% achieved HbA1c