End-stage renal disease (ESRD) incidence and prevalence, necessitating renal replacement therapy, has steadily increased. The number of patients undergoing dialysis in Korea exceeded 100,000 in 2021 and has doubled over the past decade [1]. Although mortality has declined significantly over the past 20 years, the absolute mortality risk remains higher in hemodialysis (HD) patients than in the general population [2]. Nevertheless, most patients in Korea receive HD, expensive medical service requiring sophisticated equipment, materials, several drugs, and laboratory tests, and it has significantly impacted health insurance finances [3]. The Korean health insurance system is a public, single-payer system. Notably, the National Health Insurance Act was enacted in 2000, and all insurers were merged into a single insurer [4]. Additionally, the government introduced a fixed-payment system for medical aid (MA) beneficiaries receiving HD in 2001 to promote financial stability by managing an increasing number of patients receiving HD. The government established a fixed fee for HD treatment, regardless of the type of medical institution, in order to prevent the burden on patients from increasing as the number of HD patients receiving MA increases. Additionally, the government incorporated all necessary costs, including doctors’ fees, HD fees, materials, dialysate, essential oral medications, and intravenous drugs administered during dialysis, such as erythropoietin, into one single fee and prohibited additional charges. However, there are constant concerns that the fixed-payment system’s cost is lower than the actual medical cost, causing a deficit in medical institutions, and that they may receive unequal medical services compared to National Health Insurance (NHI) beneficiaries [5]. However, only a few studies have investigated whether a difference in the treatment outcomes and mortality of patients in each group exists due to varying health insurance types, and these studies’ results are usually inconsistent [6–8]. Therefore, this study aimed to comprehensively compare the treatment process, treatment outcomes, and mortality rates according to health insurance type using the Korean Renal Data System (KORDS).

This study was approved by the Institutional Review Board of the Eulji Medical Center (No. EMC 2022-09-014). The requirement for informed consent from patients was waived due to the retrospective design of the study.

Using nationwide ESRD patient registry data from 2001 to 2017, we categorized NHI and MA beneficiaries based on health insurance type and compared demographics, treatment processes and outcomes, and mortality.

We confirmed differences between the two groups regarding demographic characteristics, age, ESRD causes, and comorbidities. The population aged ≥65 years was more prevalent in the NHI group, which was analyzed similarly in a previous study [8]. However, the dialysis vintage was longer in the MA group, indicating earlier initiation of dialysis in the MA group. Diabetes was the most prevalent cause of ESRD in both groups, followed by hypertension and chronic glomerulonephritis. Since these three diseases account for most of the diseases causing ESRD, it was possible to reaffirm the significance of managing these three diseases to prevent ESRD. Additionally, comorbidities were common in the MA group, excluding malignancy. Although there was no difference in coronary artery disease (the most prevalent cause of heart failure) between the two groups, the higher proportion of heart failure in the MA group implies that MA beneficiaries require additional management after coronary artery disease.

Regarding the treatment process, the proportion of patients using non–calcium-based phosphate inhibitors, which is a relatively expensive drug among phosphate inhibitors, was lower in the MA group than in the NHI patient group. Similarly, this prescription pattern was observed in the ESA selection. In the MA group, the erythropoietin prescription rate was high; however, darbepoetin and CERA, which are expensive drugs with high potency, were high in the NHI group. Additionally, the MA group had lower treatment goals than the NHI patient group in most treatment outcome indicators. Interestingly, considering the treatment process and treatment outcomes comprehensively, the more aggressive use of newly developed drugs may be the reason for achieving higher treatment goals in the NHI group than in the MA group. The cause of the difference in drug prescription patterns between the two groups appears to be a cost-saving measure for medical institutions. Meanwhile, there were more patients in the MA group who received dialysis three times a week. After the implementation of the fixed-payment system, medical expenses decreased by 4.7%; however, there was an increase in hospital visits per patient by 9.5%. One study analyzed that the cause of this change was a shift in medical providers’ behavior to compensate for the loss of income due to the fixed-payment system by increasing the amount of treatment [7]. Furthermore, the lower residual renal function, earlier initiation of dialysis, and longer duration of dialysis treatment among the MA group may be contributing factors. Nonetheless, these findings highlight the necessity for increased medical support in caring for this specific patient population. In response to this, the medical community has consistently argued that the government reimbursement costs are insufficient compared to the actual cost of providing better medical treatment in the MA group, and thus, the government should make additional efforts to address this constraint.

Furthermore, it was found that the MA patient group had a lower survival probability when analyzing survival between the groups, with a significant difference even when categorized by age and sex (p < 0.001). Among them, the survival rate difference between the groups was the largest in the group aged ≥65 years, which implies that healthcare intervention is crucial for those aged ≥65 years receiving HD. Conversely, when the survival probabilities of all patients were compared (Fig. 1), the difference between the two groups gradually decreased 5 years after starting dialysis, which decreased after 5 years. Furthermore, the survival probabilities converged after approximately 13 years and then reversed, considered to be affected by the survival probabilities of male patients (Fig. 2C). Therefore, additional studies are required on the factors that reduce the difference in survival probabilities, particularly the effect in male patients.

Over the past 20 years, the mortality rate of patients with ESRD has decreased to approximately one-third, with a steadily increased 5-year survival rate. However, when analyzed in this study using the health insurance type, it was confirmed that a large gap existed between the two groups. Therefore, these findings create awareness of the need to improve HD treatment quality and health equity in the MA group receiving HD and the need for active policy intervention in the MA group to reduce this difference. In general, health insurance type reflects socioeconomic status (SES), and low SES taken for granted as a risk factor for all-cause mortality in patients receiving HD [16–18]. However, the public health care system, including the MA program, exists to protect these vulnerable patients; therefore, government authorities should try to improve these issues reported.

This study had some limitations. First, because only the KORDS registry data were used to investigate demographic factors, income level, or major socioeconomic factors were excluded in this analysis. Therefore, this can be considered a limitation of the registry data; it is expected that the registration project will have to overcome this obstacle by linking it with health insurance claim data. Second, hospitals participating in the data registration project accounted for approximately 72.8% of all dialysis medical institutions. This trend occurs because there is a limit to voluntary participation in the registration project, not mandatory. Additionally, because of the investigation report’s nature, the survival rate may have been overestimated compared to the actual rate caused by factors including the death omission [19]. Third, we used the last input value as the laboratory test result. Although using a one-time test result may limit the interpretation, it was used because it could be determined that the final test value was the result that received the most medical management. Finally, this study was analyzed using data from 2001 to 2017. However, the fixed-payment system has been partially improved twice more in 2018 and 2021. In 2018, it was amended to allow separate claims even when receiving treatment for a disease other than ESRD-related complications. As a result, HD patients have improved access to medical care by eliminating the inconvenience of having to visit a medical institution again or another medical institution. Recently, in 2021, the flat-payment system was partially changed to the relative value scale system to enable rate hikes. Therefore, further research is needed to examine the impact of institutional improvements since 2018 on outcomes.

The significance of this study is as follows: First, it is the first study to comprehensively compare and analyze the treatment process, outcomes, survival, and death by groups based on the health insurance type employing the representative KORDS data of Korean patients who received HD. Second, whereas the treatment indicators between the two groups were compared only with a simple average value in the previous study, we evaluated the overall patient management status between the two groups by further comparing the goal achievement rate suggested using international guidelines. Third, the prescription patterns of specific HD-related drugs in domestic patients undergoing HD were analyzed and compared between groups according to health insurance type. Therefore, this study is meaningful because it was possible to confirm the difference in the prescription for each type of drug between the two groups in the actual clinical field. Finally, this study has important significance by providing evidence for improving healthcare policies and systems to enhance health equity among MA beneficiaries.