Introduction

In the recent decades, health-related quality of life (HRQOL) has been widely accepted as a valid marker of both treatment outcome and mortality for patients with chronic diseases [1, 2]. It is also considered as a consistent and powerful predictor of health outcomes in end stage renal disease (ESRD) [3–9]. It is generally agreed that HRQOL of dialysis patients is usually poorer than that of the age-matched subjects from the general population, because of the typically high burden of comorbidity and complications of ESRD [3].

Recently, there has been increasing interest in factors impacting on HRQOL of ESRD patients, but it has not been clearly confirmed yet which of them showed the strongest influence on the patients’ HRQOL [9–13]. Generally, ESRD patients are in great need for self-management of long-term illnesses and must frequently make daily decisions involving fluid intake, nutrition, physical activity, and symptom management [13–15]. Additionally, self-efficacy and treatment satisfaction are known to influence these self-management and decision-making processes [16–18]. Until now, several previous studies have dealt with self-efficacy [19–22] and treatment satisfaction [23, 24], but most of them used SF-36 and showed limitation in considering disease-specific HRQOL.

Therefore, the purpose of this study was to measure the level of HRQOL using KDQOL-36 and to reveal the association of self-efficacy and treatment satisfaction with HRQOL in Korean patients with ESRD.

Subjects and methods

Subjects

The prevalent dialysis patients, including both hemodialysis (HD) and peritoneal dialysis (PD) patients from two university hospitals, had been included from February to June in 2010. Patients who were on the dialysis for acute kidney injury were excluded from the study. The Institutional Review Board of Kyungpook National University Hospital approved the research protocol [IRB Number: KNUH_09_1045]. All subjects gave written informed consent before study enrollment.

Instruments

We investigated the socio-demographic factors, treatment satisfaction, self-efficacy and HRQOL by self-administrative questionnaire and dialysis-related factors by reviewing the clinical records.

Self-efficacy was composed of 11-items with 2 subscales (i.e., 7 items for treatment goal self-efficacy and 4 items for treatment management self-efficacy). The items were modified from those referring to empowerment of diabetes patients [18]. Responses were on 5-point Likert scales; we used mean scores (range: 1–5). The modified scale used in this study demonstrated adequate content validity and internal consistency reliability (Cronbach’s alpha = 0.90 and 0.86, respectively). Construct validity was supported by factor analysis, and the result was that self-efficacy was composed of two subscales.

The 10-item questionnaire asked about treatment satisfaction during dialysis. Responses were on a 7-point Likert scale where 0—strongly disagree and 6—strongly agree. Scores were summed and ranged from 0 to 60. In this study, the internal consistency coefficient (Cronbach’s alpha) was 0.88 and factor analysis resulted in all items loading greater than 0.42 on a single factor.

The Korean version of the KDQOL-36 includes 12 items that provide a generic chronic disease core (i.e., the SF-12, a shorter version of the SF-36), as well as 24 additional items (i.e., kidney-disease-targeted items). The 24 additional items focus on particular health-related concerns of individuals with kidney disease (i.e., symptom/problem list, 12 items; effects of kidney disease, 8 items; and burden of disease, 4 items). The item scores were aggregated without weighting and transformed linearly to a 0–100 possible range, with higher scores indicating better states, which resulted in a total of dimensions.

Statistical analysis

To compare scores of HRQOL subscales by socio-demographic and disease-related factors, the Student’s t test and analysis of variance were used. The associations of self-efficacy and treatment satisfaction with HRQOL subscales were assessed using Pearson correlation coefficients. To assess these associations after adjusting for possible confounders, multiple linear regression analyses were performed. Selected confounders were age, sex, educational level, job, dialysis method, dialysis duration, causes of ESRD, dialysis adequacy, comorbidity, and serum albumin level. The SPSS 15.0 statistical package for Windows (SPSS, Chicago, IL) was used for all statistical analyses.

Results

A total of 237 patients were recruited in this study, including 172 (72.6 %) HD patients and 65 (27.4 %) PD patients.

Their socio-demographic and disease-specific characteristics are shown in Tables 1 and 2, respectively. Overall, 54.0 % were male, 27.8 % younger than 49 years, 24.9 % 50–59 years, 26.2 % 60–69 years, and 21.1 % older than 70 years. In the disease-specific characteristics, 61.0 % received dialysis treatment for more than 2 years and diabetes mellitus was the most common (39.7 %) cause of ESRD, followed by hypertension (29.1 %) and glomerulonephritis (10.5 %).

Table 1 Health-related quality of life (HRQOL) scores by general characteristics (unit: mean ± SD)
Full size table
Table 2 HRQOL scores by disease-specific characteristics (unit: mean ± SD or Pearson’s correlation coefficient)
Full size table

The mean HRQOL results in 5 domains were as follows: PCS score was 39.1 ± 9.5; MCS, 44.6 ± 6.8; symptom/problem list, 67.6 ± 17.1; effect of disease, 58.5 ± 19.6; and burden of disease, 41.1 ± 28.4 (Table 1). In PCS, female, older, less-educated, and jobless patients, with stroke or diabetes mellitus, reported significantly lower QOL than the others (p < 0.05). In symptom/problem list, patients in PD reported significantly lower QOL than the others (p < 0.01), and factors associated with burden of disease were the cause of ESRD and the number of co-existing diseases (p < 0.05). Serum albumin showed positive correlation with both PCS and effects of disease (p < 0.01). Among all patients, the mean treatment goal self-efficacy was 3.1 ± 0.6; treatment management self-efficacy, 3.2 ± 0.6; and treatment satisfaction, 32.7 ± 11.4, respectively (Table 3). Treatment goal self-efficacy showed positive correlation with PCS, symptom/problem list, effects of kidney disease, and burden of kidney disease, whereas treatment management self-efficacy correlated with symptom/problem list and effects of disease (both p < 0.05). Treatment satisfaction showed positive correlation with PCS and effects of disease (both p < 0.05).

Table 3 Correlation between self-efficacy, treatment satisfaction, and HRQOL (unit: Pearson’s correlation coefficient)
Full size table

After adjusting for confounders, both treatment goal self-efficacy and treatment management self-efficacy significantly correlated with all 5 domains, except PCS. Treatment satisfaction was significantly related with PCS, MCS, and effects of kidney disease (Table 4).

Table 4 Association of self-efficacy, treatment satisfaction, and HRQOL by multiple linear regression analysis
Full size table

Discussion

In this study, we measured the HRQOL of dialysis patients, including both HD and PD. In comparison between PD and HD patients, we could find significant difference only in symptom/problem list (i.e., HD patients reported lower QOL than PD patients). There have been several studies using KDQOL-36 for evaluating the HRQOL of patients with chronic kidney disease [25–27], but few studies were conducted in dialysis patients [28]. Compared to QOL results from other studies [25, 28], ours were very similar in PCS, MCS, and Effect of disease. However, some differences were observed in the other domains: We report lower scores in symptom/problem list and higher scores in burden of disease. Restricting to the HD patients, our results were also very similar with the results of the Dialysis Outcomes and Practice Patterns Study [27], which was a prospective, observational, multinational study for HD patients, using KDQOL-SF™.

In our study, dialysis patients showed higher scores in MCS than in PCS, and this has been also reported in several previous studies [25–30]. In other words, despite the worsening of the physical health status, the mental health of dialysis patients is relatively preserved. This was previously explained by dynamic adaptation of patients’ expectations to their chronic illness [11, 30].

We also evaluated whether the self-efficacy and treatment satisfaction, respectively, could impact on the HRQOL of dialysis patients. In this study, after adjusting for the confounders’ effect, self-efficacy on both treatment goal and treatment management showed significant positive association with HRQOL in almost all domains, except PCS. Oh-Park et al. [22] reported positive association between self-efficacy and HRQOL in MCS. Therefore, it remains to be seen whether self-efficacy may influence HRQOL in the generic and disease-specific domains.

Finally, treatment satisfaction was positively associated with HRQOL in PCS, MCS, and effects of disease. These associations are supported by Callahan’s study [23], reporting that patients’ participation in care planning could lead to increased treatment satisfaction and increased HRQOL scores. This implies that high treatment satisfaction can improve patients’ compliance and control disease more effectively, consequently leading to better HRQOL and decrease mortality rate.

Our study has several limitations. First, our participants were volunteer outpatients recruited in two university hospitals; therefore, they had some difference with the general dialysis patients especially in their socio-economic characters and disease severity, and these differences might modified their perception of QOL. Therefore, our results must be applied to general dialysis patients with caution. Second, the instruments, the Korean version of KDQOL-36, self-efficacy and treatment satisfaction questionnaires that we used have not been validated yet.

In spite of those limitations, to the best of our knowledge, this is the first study to use KDQOL-36 for evaluating HRQOL of dialysis patients and to investigate the impact of self-efficacy and treatment satisfaction on HRQOL in Korea.

This study has main findings. First, regular and systematic monitoring for dialysis patients’ HRQOL must be considered as an effective tool of quality control in dialysis care in Korea. Secondly, self-efficacy and treatment satisfaction independently influenced HRQOL in almost all domains. Therefore, interventions to increase self-efficacy and treatment satisfaction should be considered in caring for patients with ESRD.