Exploring Variation in Glycemic Control Across and Within Eight High-Income Countries: A Cross-sectional Analysis of 64,666 Children and Adolescents With Type 1 Diabetes

Abstract

Objective: International studies on childhood type 1 diabetes (T1D) have focused on whole-country mean HbA_1c levels, thereby concealing potential variations within countries. We aimed to explore the variations in HbA_1c across and within eight high-income countries to best inform international benchmarking and policy recommendations.

Research design and methods: Data were collected between 2013 and 2014 from 64,666 children with T1D who were <18 years of age across 528 centers in Germany, Austria, England, Wales, U.S., Sweden, Denmark, and Norway. We used fixed- and random-effects models adjusted for age, sex, diabetes duration, and minority status to describe differences between center means and to calculate the proportion of total variation in HbA_1c levels that is attributable to between-center differences (intraclass correlation [ICC]). We also explored the association between within-center variation and children's glycemic control.

Results: Sweden had the lowest mean HbA_1c (59 mmol/mol [7.6%]) and together with Norway and Denmark showed the lowest between-center variations (ICC ≤4%). Germany and Austria had the next lowest mean HbA_1c (61-62 mmol/mol [7.7-7.8%]) but showed the largest center variations (ICC ∼15%). Centers in England, Wales, and the U.S. showed low-to-moderate variation around high mean values. In pooled analysis, differences between counties remained significant after adjustment for children characteristics and center effects (P value <0.001). Across all countries, children attending centers with more variable glycemic results had higher HbA_1c levels (5.6 mmol/mol [0.5%] per 5 mmol/mol [0.5%] increase in center SD of HbA_1c values of all children attending a specific center).

Conclusions: At similar average levels of HbA_1c, countries display different levels of center variation. The distribution of glycemic achievement within countries should be considered in developing informed policies that drive quality improvement.

Figure 1

Between-center variation in HbA_1c across countries. Center means derived from linear fixed-effects regression models adjusted for patient characteristics (sex, age, duration of diabetes, and minority status). A: Boxplots showing center variation in adjusted mean HbA_1c across eight countries. The shaded box represents the interquartile range capturing the middle 50% of the centers. Whiskers extend to include centers within 1.5 times the interquartile range beyond the upper and lower quartiles; dots outside the whiskers represent outlying centers; crude national average HbA_1c values are represented by diamonds. B: Kernel-smoothed distribution of adjusted center HbA_1c means by registry/audit. The dashed vertical line represents the ISPAD glycemic target recommended for children with diabetes.

Figure 2

Country mean HbA_1c before and after adjustment for cross-country differences in the characteristics of children (age, sex, diabetes duration, and minority status) and center effects. Estimates of adjusted country means derived from a two-level model with a random effect for center including data from all eight countries.