Secular trends in HbA1c levels among children and adolescents with type 1 diabetes.

Introduction: The management of type 1 diabetes (T1D) has significantly improved over the past two decades in parallel with advancements such as medical nutrition therapy, long-acting and rapid-acting insulin analogues, reimbursement for blood glucose test strips for T1D in Taiwan, and the widespread use of continuous glucose monitoring (CGM). This study aimed to evaluate whether glycemic control has improved among children and adolescents with T1D at MacKay Children's Hospital and Hsinchu MacKay Memorial Hospital from January 1, 2000, to December 31, 2023, and to investigate whether trends varied by sociodemographic factors. Materials and methods: We analyzed electronic medical records of 688 patients with T1D, registered between 1st, Jan, 2000 and 31th, Dec, 2023 from MacKay Children's Hospital and Hsinchu MacKay Children's Hospital, which contained repeated measures of HbA1c. HbA1c levels and achievement rate of optimal HbA1c level, defined as HbA1c <7.0%, were treated as outcome variables for analysis. A linear mixed-effects model (LME) with a random intercept per patient was used as the primary analytic approach to estimate the calendar-year trend in HbA1c, adjusting for diabetes duration at each visit, sex, DKA status, and age group at diagnosis. Formal interaction terms between calendar year and each subgroup variable were tested using likelihood ratio tests (LRT). For the binary outcome of HbA1c <7.0%, a generalized estimating equations (GEE) approach with an exchangeable correlation structure was applied. All analyses were performed using R software (version 4.3.2). Results: In the LME, HbA1c declined significantly over the study period after adjusting for diabetes duration and patient characteristics (β = -0.037% per year, 95% CI -0.053 to -0.021, p < 0.001), corresponding to an estimated overall decrease of approximately 0.84% over 23 years. The annual mean HbA1c decreased from 9.17% in 2000 to 7.99% in 2023. Formal interaction testing revealed that the rate of HbA1c improvement differed significantly by sex (LRT p = 0.002), DKA status at presentation (LRT p < 0.001), and age group at diagnosis (LRT p < 0.001). Female patients and those without DKA at presentation showed more pronounced calendar-year improvements. Adolescents diagnosed at 12-18 years consistently exhibited the highest HbA1c levels (β = +0.790% vs. 0-6 yr group, p < 0.001), but also showed the steepest rate of improvement (β = -0.084%/yr). The proportion of HbA1c measurements below 7.0% showed a statistically significant increase per GEE analysis (OR = 1.029 per year, 95% CI 1.011-1.047, p = 0.002), although the annual achievement rate trend did not reach significance by Kendall's tau (τ = 0.16, p = 0.29). Conclusions: HbA1c levels among children and adolescents with T1D showed a statistically significant declining trend over 23 years at two centers in Taiwan, in parallel with the progressive adoption of diabetes technology and evolving NHI policy. The rate of improvement differed significantly across subgroups defined by sex, DKA status at presentation, and age group at diagnosis. Despite overall improvement, the 12-18 year age group consistently maintained the highest HbA1c levels throughout follow-up, and the youngest (0-6 year) group showed no significant secular improvement, highlighting persistent clinical challenges across developmental stages.