BackgroundThe comorbidities of ischemic stroke (IS) are increasing worldwide. This study aimed to quantitatively assess the effect of different types of comorbidity on readmission and hospitalization expenditures of patients with IS. MethodsA retrospective observational study was conducted from the basic insurance claims database of a large city in China, between January 1, 2018, and May 31, 2022. We identified patients with IS aged 18 years and over, who experienced the first episode of IS and had one-year follow-up records. This study divided eighteen different comorbid conditions into two categories (concordant comorbidity and discordant comorbidity) and the IS patients were further categorized into four groups. Multivariable logistic regression models and generalized linear models with log-link and gamma distribution were to estimate the effect of different comorbidity groups on one-year readmission rates and annual hospitalization expenditures. ResultsIn total, 99,649 adult patients with IS were identified. Approximately 94.0% of patients with IS had at least one comorbidity, and 63.8% reported concordant comorbidity only. Patients with IS had a readmission rate of 26.7%, and the mean of annual hospitalization expenditure and annual hospitalization out-of-pocket expenditure (OOPE) were 28086.6 Chinese Yuan (CNY) and 8267.3 CNY, respectively. After adjustment for covariates, the concordant comorbidity-only group had the highest readmission rate, annual hospitalization expenditure, and OOPE compared with the other groups, furthermore, these results increased as the number of comorbidity increased and had statistically significant positive associations. ConclusionsThe readmission and annual hospitalization expenditures of patients with IS were associated with different comorbidities. Concordant comorbidity increased hospital readmission risk and health expenditures. To better manage the comorbidities of patients with IS, especially concordant comorbidities, it is necessary to establish a routine care strategy specifically for comorbid conditions.