Modification effect of receipt of diabetes care on the association between COVID-19 infection and HbA1c level during the first year of the coronavirus pandemic using a nationwide population-based database

Aims/introduction: We assessed the modification effect of adherence to diabetes care on the association between HbA1c levels and the risk of coronavirus disease 2019 (COVID-19) among individuals with diabetes using a population-based database. Material and methods: We retrospectively identified individuals with diabetes during routine health checkups performed in 2019 in Japan using a population-based claims database (JMDC, Tokyo, Japan). We assessed the risk of COVID-19 infection in 2020 in relation to HbA1c levels during routine checkups, stratified by the presence/absence of follow-up for diabetes care in 2019. Several sensitivity analyses were performed. Results: We identified 65,956 individuals with an HbA1c >= 6.5% and fasting glucose >= 126 mg/dL in routine checkups, including 52,637 and 13,319 with and without at least one physician consultation for diabetes care in 2019, respectively. Although high HbA1c levels were associated with an increased risk of COVID-19 infection in a dose-dependent manner among individuals without diabetes care in 2019 (odds ratios, 1.53 and 2.17 in individuals with HbA1c of 7.0-7.9% and >= 8.0%, respectively) with a reference to HbA1c of 6.5-6.9%, individuals with diabetes care had no such trend in 2019 (odds ratios, 0.99 and 0.97 among individuals with HbA1c of 7.0-7.9% and >= 8.0%, respectively). Sensitivity analyses yielded consistent results when the variable definitions were changed and after multivariable adjustment with multiple imputation. Conclusions: This population-based study suggests that adherence to diabetes care may modify the association between HbA1c levels and the risk of COVID-19 infection.