Comparison of catastrophic out-of-pocket medical expenditure among older adults in the United States and South Korea: what affects the apparent difference?

BACKGROUND: Medical spending rises sharply with age. Even with universal health insurance, older adults may be at risk of catastrophic out-of-pocket medical spending. We aimed to compare catastrophic out-of-pocket medical spending among adults ages 65 and older in the United States, where seniors have near-universal coverage through Medicare, versus South Korea, where all residents have national health insurance. METHODS: We used the 2016 Health and Retirement Study and the Korean Longitudinal Study of Aging. The study population were adults ages 65 and over in the US (n = 9,909) and South Korea (n = 4,450; N = 14,359). The primary outcome of interest was older adults’ exposure to catastrophic out-of-pocket medical expenditure, defined as out-of-pocket medical spending over the past two years that exceeded 50% of annual household income. To examine the factors affecting catastrophic out-of-pocket medical spending of older adults in both countries, we performed logistic regression analyses. To compare the contribution of demographic factors versus health system-level factors to catastrophic out-of-pocket medical spending, we performed a Blinder-Oaxaca decomposition. RESULTS: The proportion of respondents with catastrophic out-of-pocket medical expenditure was 5.8% and 3.0% in the US and South Korea, respectively. A Blinder-Oaxaca decomposition showed that the difference in the rate of catastrophic out-of-pocket medical expenditure spending between the two countries was attributable largely to unobservable system-level factors, rather than observed differences in the sociodemographic characteristics. CONCLUSIONS: Exposure to catastrophic out-of-pocket medical spending is considerably higher in the US than South Korea. Most of the difference can be attributed to unobserved health system-level factors. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12913-022-08575-1.