The prevalence of end-stage kidney disease (ESKD) is increasing worldwide every year, and healthcare expenditures for dialysis treatment continue to expand [1]. Most ESKD patients already have multiple comorbidities before they start dialysis, including heart disease, cerebrovascular disease, diabetes mellitus, and hypertension [2]. Even after starting dialysis, complications can occur in almost all organs, including the heart, lungs, brain, blood vessels, and digestive system. Because the morbidity and mortality rates of ESKD patients are higher than those of the general population, it is very important to have professional personnel as well as proper facilities and equipment in hemodialysis (HD) units [3,4].

However, despite the rapid increase in the number of ESKD patients and subsequent increase in the number of HD centers, some HD centers still lack sufficient personnel and facilities, threatening the health of patients in Korea [5,6]. In response, the Korean Society of Nephrology (KSN) introduced the HD unit accreditation program in 2016 to recommend and evaluate standard practice guidelines for the safe treatment of HD patients and to manage the quality of HD facilities [7].

A few hundreds of hospitals received their initial qualified dialysis center (QDC) certification in the past few years. Since several years have passed after the HD unit accreditation program was launched, questions have been raised about whether QDCs have better outcomes than non-QDCs and, more importantly, whether the action toward QDC certification improves the outcome of HD treatment. There have been papers on the effect of certification program on patient prognosis in other diseases such as stroke center certification [8], but no research has been conducted on the impact of HD unit certification on patient mortality. To address this point, we compared all-cause mortality of the patients in HD centers who received QDC certification between 2016 and 2018 with those in HD centers without QDC certification (non-QDCs).

This observational study showed that maintenance HD patients in QDC have a 10% lower mortality risk compared to the non-QDC group. The patients in QDC showed lower serum calcium and phosphorus levels, and higher Hb and single-pool Kt/V levels compared to the non-QDC group. However, when we adjusted covariates, the QDC group remained an independent factor for survival.

Many countries have their own approval and/or accreditation programs for HD units [3]. Approval involves the evaluation of several criteria before the establishment of an HD unit. On the other hand, an accreditation program involves the evaluation of maintaining professional personnel, proper facilities, equipment, and services after the establishment of HD units. In the United States, the Survey and Certification Program certifies HD facilities for inclusion in the Medicare Program by evaluating whether each facility meets specified safety and quality standards [9]. The United States government also delegates its role to the ESRD Network, an autonomous organization for quality control and monitoring, to ensure that these facilities continue to meet these basic requirements [10]. Korea, like Japan, does not have an obligatory program for approval or accreditation operated by the Korean government. The lack of standards for approval or accreditation systems may threaten patient health. Although Korean HIRA collects data from all HD units periodically for the evaluation of HD adequacy, it is insufficient to investigate the real-world practice in HD units. For example, some HD units may provide low-quality HD service due to the heavy workload of staff or even provide unethical solicitation to recruit more patients [5,11,12]. Instead, KSN has set up the accreditation program and voluntarily has operated the program since 2016. The evaluation criteria for the accreditation program not only include structure (staffing, facility, and equipment) and HD process (HD adequacy test and regular inspection) but also include ethical aspects (solicitation to recruit patients or providing free transportation) and official records of patient events (death and transfer) [3,7]. The HD unit accreditation program, however, was set up to guide the minimum requirement for HD treatment. Therefore, the program collects whether or not the institution passes certain goals to operate adequate HD treatment.

This study is important to understand whether the self-regulated accreditation program by KSN improves clinical outcomes and reduces mortality in HD patients. Our study suggested that the patients treated in the QDC may have better patient survival and clinical outcomes. Individual characteristics such as age, comorbidities, and nutritional status can be important factors that determine clinical outcomes in HD patients [13]. A previous study by Owen et al. [14] showed that low serum albumin concentration is an important predictor of patient death showing an odds ratio of 1.48 in those with serum albumin concentration of 3.5 to 3.9 g/dL and 3.13 for those with serum albumin concentration of 3.0 to 3.4 g/dL compared to those with normal serum albumin concentration over 4.0 g/dL. Serum albumin concentration was a stronger risk factor compared to the urea reduction ratio. Diabetic patients had lower patient survival due to lower serum albumin concentration and lower urea reduction ratio. The other study performed by Combe et al. [15] also showed that patient survival was significantly influenced by age, the presence of diabetes mellitus, and serum albumin concentration, but not by other variables, including Kt/V and urea reduction ratio. Our study also demonstrated that age and serum albumin concentration affect patient mortality but not Kt/V. However, a recent study by Ajmal et al. [16] demonstrated that facility-level quality control is also an important factor for patient mortality among incident HD patients. In their study, the dialysis facilities with lower Quality Incentive Program (QIP) performance scores, which may be compared to our non-QDC group in the HD unit accreditation program, showed higher patient mortality. The patients with QIP scores <45 (HR, 1.39) and 45 to <60 (HR, 1.21) had higher patient mortality rates than those in the facilities with scores ≥90. The patients with lower QIP scores did not demonstrate differences in age and sex but showed significant differences in BMI and underlying comorbidities (diabetes mellitus, ischemic heart disease, heart failure, and cerebrovascular accident). Our study also showed significantly higher BMI and higher prevalence of comorbidities in the patients in the non-QDC group. Our study also demonstrated lower serum calcium and phosphorus and higher plasma Hb and single-pool Kt/V in the QDC group. These findings can be interpreted as individual characteristics. On the other hand, they can be the results of facility-level quality control among QDC. Our previous study demonstrated that structural and procedural indicators are important for the survival of HD patients [6]. Specifically, a high nurse caseload was associated with high patient mortality in HD units [11]. Dialysis specialist care was also an important determinant of overall patient survival [17]. In addition to adequate staffing, the environmental impact of HD can be essential [18]. Monitoring and maintaining laboratory parameters in adequate ranges can also be essential [16,19]. Although we did not analyze the effect of each component in the accreditation program upon clinical outcomes, HD facilities in the QDC group are likely to make an effort to improve structural and procedural dimensions. In addition to facility-level quality control, ethical components can be important for patient outcomes. Previous report showed that the overall mortality rate in incident HD patients was higher in soliciting facilities compared to non-soliciting facilities [5]. The soliciting facilities are likely to reduce costs by minimizing the dialysis time or using cheaper and less effective equipment or medication.

It is true that baseline profiles of the HD patients were better for patient survival: younger age, lower proportion of diabetes mellitus, better laboratory parameters, and HD adequacy. However, when we adjusted them in multivariate Cox regression analysis, the QDC group was an independent predictor for patient survival. While individual characteristics are not modifiable, we may improve each component in the accreditation evaluation by efforts. Further prospective interventional studies are needed to confirm whether facility-level accreditation improves patient outcomes.

The elderly patients (≥65 years), those with cerebrovascular accidents, or those on Medicaid insurance were unlikely to get benefits from QDC. It is likely that age and history of cerebrovascular accident are stronger risk factors for mortality in the elderly population. The patients on Medicaid insurance were small population and our result cannot be generalized for the Medicaid population. The characteristics of individual patients may have a greater impact on clinical outcomes than the status of accreditation in these subgroups.

There are several limitations in our study. The follow-up duration for mortality analysis is only 35.6 months. Since the HD unit accreditation program launched in 2016, the long-term benefit of the accreditation program should be evaluated in the future. In addition, the effect of each indicator in the accreditation program on patient mortality was not evaluated further. Whether improvement in each indicator results in improved patient survival should be elucidated in the future study. Finally, the certified institutions are more likely to participate in HD unit accreditation programs and therefore there may be a selection bias. The gap between the qualified centers and non-qualified centers can be larger than the presented data. However, we have utilized a multivariate Cox hazards model to adjust possible confounders.

However, this is the first study to evaluate the clinical utility of the HD unit accreditation program in Korea. The accreditation or certification programs on specific diseases or procedures may motivate physicians to improve standard care which may improve patient outcomes [8]. In order to implement basic standards of care in HD units, there should be continuous, cooperative efforts from government body, KSN, and related organizations.