Association between Multimorbidity and Catastrophic Health Expenditure among Older Adults: A Focus on Socioeconomic Differences

Background: Although multimorbidity increases healthcare utilization and the financial burden, evidence of its association with catastrophic health expenditure (CHE) across income groups among older Koreans remains limited.This study examined the association of multimorbidity with healthcare utilization and CHE, and whether the association differs by the household income level.Methods: This study used data obtained from waves 7-9 (2018, 2020, and 2022) of the Korean Longitudinal Study of Ageing and included 3,015 adults aged ≥50 years.Multimorbidity was defined as having two or more of eight noncommunicable chronic diseases, while excluding mental and memory disorders to minimize recall bias and ensure measurement consistency.CHE was defined as out-of-pocket health spending that exceeded 10% of the total household consumption.The determinants of multimorbidity and the association between the number of diseases and the occurrence of CHE were examined using a random-effects logistic regression model; moreover, the relationship between the number of diseases and healthcare utilization was analyzed using a negative binomial regression model.A generalized linear mixed model was used to account for repeated individual-level observations.Results: A greater number of chronic conditions was associated with more outpatient visits, longer hospital stays, and a higher risk of CHE.The risk of CHE increased substantially with decreasing socioeconomic status, with the highest CHE risk observed in the lowest income group (odds ratio=4.99,95% confidence interval: 3.29-7.58).On income-stratified analyses, the association between multimorbidity and CHE was most pronounced in the middle-income group and was attenuated in the highest-income group, which suggests an exploratory nonlinear pattern that warrants further investigation. Conclusion:The association between multimorbidity and CHE in older adults may differ by their socioeconomic status.The findings should be interpreted as associations rather than causal effects and may inform further discussions on financial protection for vulnerable populations who may experience increased multimorbidity-associated healthcare utilization and financial burden.