Background
Chronic kidney disease (CKD) has become a major global health issue, affecting around 10-13% of the adult population in countries such as the US [
1], Taiwan [
2], and China [
3]. Owing to the progressive nature of CKD, patients with CKD are at a high risk of gradually progressing to end stage renal disease (ESRD). The estimate in current available reports is that approximately 1.9 million ESRD patients around the world are receiving renal replacement therapy (RRT); the figure does not capture the proportion of ESRD patients without access to RRT treatment [
4]. Life-long dialysis and kidney transplantation are treatment choices for patients with ESRD to sustain their lives. These patients suffer from the signs and symptoms of relapse, experience fear and anxiety, and face financial burdens, causing an impaired quality of life [
5]. In mainland China, the number of CKD patients was estimated to be around 119.5 million based on a national survey in 2010 [
3]. Data from the Chinese Renal Data System revealed that there were about 270,000 patients undergoing haemodialysis (HD), while only 30,000 were received peritoneal dialysis (PD) treatment at the end of 2012 [
6], suggesting that HD is the major treatment modality in China, accounting for approximately 90% of the total ESRD patients.
Chronic kidney disease is a progressive disease. Patients with CKD experienced impaired health-related quality of life (HRQOL) [
7‐
9], as both the renal disease itself and its treatment have long-term impacts on lifestyle. Accumulating studies have generated evidence to support the relationships between impaired HRQOL and clinical outcomes, such as increased hospitalization and mortality, in CKD population [
10‐
12]. Attention has recently focused on effects to improve the HRQOL of persons with CKD. HRQOL is increasingly being chosen over laboratory data as the primary outcome measure in clinical research [
13] when examining the effects of treatment, because an improvement in HRQOL would bring greater fulfillment to the lives of patients [
10]. The routine use of HRQOL measures creates an opportunity for health care providers to incorporate the experiences of patients when developing interventions that best suit their needs given the patients’ adverse life circumstances [
14], and to support patient-centered treatment decisions [
15].
The Kidney Disease Quality of Life (KDQOL™) questionnaire combines the generic SF-36 instrument and disease-specific components for assessing the HRQOL of CKD patients. The original questionnaire consists of 134 items, and takes about 30 minutes to complete [
16]. The authors further developed a short version – the KDQOL-SF™ version 1.3 – which includes 43 items focusing on kidney disease and SF-36 [
17]. The KDQOL-SF™ has been translated into many languages including Chinese. The latest abbreviated version – KDQOL-36™ – is even briefer making it more likely that patients will respond to the questionnaire [
18]. The brief version has also been found to be suitable for use in routine evaluations of quality of care in busy practice settings [
19] and has been used extensively to evaluate CKD patients in different stages of the disease, including patients who are receiving dialysis treatment [
20].
The Mandarin Chinese version of the scale was translated by Amgen, Inc. and the MAPI Institute and can be downloaded from the website of the RAND Corporation [
21] for non-commercial use. The translation process followed the specific guidelines stipulated by the RAND health [
22]. Forward and back forward translations were adopted to ensure the equivalence between the original English version of the KDQOL-36™ and the translated Mandarin Chinese version. The psychometric properties of the translated version of the scale have not been evaluated or reviewed by RAND. Chinese comprise 19% of the world’s total population. The number of patients in China with CKD is estimated to be about 119.5 million [
3]. A valid Chinese version of the KDQOL-36™ will enable researchers to examine the quality of life of CKD patients within the country and allow for cross-country comparisons to be made. To address this need, the aim of the study was to determine the validity and reliability of the KDQOL-36™ with a Chinese population.
Discussion
Mandarin Chinese is spoken by around 850 million people in China, Taiwan, and Southeast Asia, as well as in the US, Canada, New Zealand, Peru, and South Africa [
50]. This study is the first validation study of the KDQOL-36™ questionnaire to have been conducted in China. It has demonstrated that the Mandarin Chinese version of the scale is linguistically and culturally relevant to Chinese CKD patients. The ceiling and floor effects were less than 20%, suggesting that the instrument can capture the full range of potential responses in CKD population [
51].
Lynn [
52] recommended that if five or fewer experts give a rating, the I-CVI must be 1.0. An S-CVI of 0.8 or higher is considered acceptable [
32]. Both the I-CVI and S-CVI were 1.0. The results indicated that all items of the Mandarin Chinese version of KDQOL
™-36 were considered to be appropriate and relevant, giving evidence of the excellent content validity. During the content validity process, ‘walking’ and ‘playing Tai Chi’ were used in place of the problematic examples. Similar amendments were reported for different versions of the KDQOL-36™, such as the Korean [
53], Filipino [
45], Portuguese [
54], and Egyptian [
55] versions.
The convergent validity of the KDQOL-36™ was supported by the hypothesis that those patients who experienced better quality of life had a higher overall health rating. The overall health rating reflects the individual’s feelings and provides an estimate of the subjective perception of one’s health status [
33]. Substantial correlations were observed between overall health and the subscales for Symptoms and problems, Burden of kidney disease, and PCS (P < 0.01), confirming that the KDQOL-36™ and the overall physical health rating are conceptually related. These results are consistent with studies that have validated versions of the KDQOL™ instrument in other languages, such as the Korean [
53], Singaporean [
56], Greek [
57] and Iranian [
51] versions. It was noted that the non-substantial correlation between the MCS score and the overall health score could be related to how an individual perceived his/her overall health. Previous studies have suggested that amongst the general adult population, the overall health rating principally reflects the physical dimension of health [
58]. Moreover, there was a non-substantial correlation between the Effects of kidney disease and the overall health rating. As ESRD patients were getting used to the idea that they would need life-long treatment [
26], living on dialysis had become their ‘normal way of being’ [
59]. To help them to increase their confidence in maintaining their health, some patients even considered dialysis to be a ‘part-time job’ [
5]. On the other hand, patients who were receiving dialysis could not avoid fluid or dietary restrictions even if their condition had improved. Therefore, changes in the patients’ perception of their overall health might not have a direct or strong relationship with the Effects of kidney disease, which is consistent with our results.
The convergent validity of the KDQOL-36™ was also supported by the hypothesis that patients with lower subscale scores in the KDQOL-36™ would report a higher BDI-II score. All of the disease-specific domains and the MCS showed substantial inverse correlations with the BDI score. Similar findings were reported in previous studies, showing that depressive symptoms among the CKD population were strongly associated with poor health-related quality of life in multiple domains [
34,
35]. A relatively low correlation was found between the PCS domain and the BDI score. A possible explanation for this is that our diverse patient groups experienced different stressors. The psychological stress of patients who had not yet commenced dialysis treatment might not have been related to impaired physical functioning, but to obligatory hospital visits or to the fear of becoming dependent on dialysis [
60]. The positive correlations coefficients between the kidney disease targeted scales and two main composite summaries from SF-12 demonstrated that the two components (generic core and disease-targeted core) of the KDQOL-36™ are conceptually related. The significant association presented in this study further supports the construct validity of the KDQOL-36™, and is in agreement with the results reported in other validation study [
55].
The KDQOL-36™ demonstrated evidence of known-group validity as the scale scores were able to discriminate between subgroups of patients. In our study, females, the unemployed, patients with complications, and patients who had undergone dialysis for a longer duration tended to have worse HRQOL. The results corroborated those of previous studies evaluating the quality of life of CKD patients, where gender, employment status, comorbidities, and dialysis duration were shown to influence HRQOL scores [
39,
40,
58,
61,
62]. Contrary to our expectations, there were no significant differences in any of the KDQOL-36™ subscale scores among those of different age groups. A possible explanation for this is that more young patients were recruited in our study, with only 20.4% of the participants being older than 60. In addition, the hypothesis that dialysis patients experience a lower HRQOL than those who have not yet commenced dialysis was not supported. This could be due to the fact that the non-dialysis CKD patients recruited in our study were hospitalized, while the dialysis patients were not. Hospitalized patients experience a low HRQOL [
63]. Hence, the HRQOL of those hospitalized non-dialysis patients might be lower than that of outpatients who are receiving dialysis, which is consistent with our findings.
For test-retest reliability, an ICC of 0.70-0.86 demonstrated the stability of the scale over time [
30]. The Cronbach’s alpha values suggested that the scale is internally reliable. The internal reliability of all of the subscales exceeded 0.7, with the PCS (0.69) approaching the minimum desirable standard. Acceptable levels of internal consistency suggested that all of the items from each subscale of the KDQOL-36™ fit together conceptually and measure the same construct [
42].
Conclusions
The results of our present study support the claim that the Mandarin Chinese version of the KDQOL-36™ is easy to understand and demonstrates good validity and reliability. The evidence supports the view that the questionnaire is culturally appropriate for use in Chinese populations with CKD, and can be adopted by both researchers and health care providers who are interested in understanding and designing interventions to improve the quality of life of patients.
There were some limitations to this study. First, the patients were recruited from a single study site, which may limit the generalizability of the findings. Second, the testing was conducted among a mixed sample of CKD patients with no even distribution according to age. Due to the limited sample size, this could suggest the existence of bias, as the younger patients tended to report a higher HRQOL. The study was conducted using a mixed sample of CKD patients. Although including a wide range of patients allowed variations in quality of life measures, it affected the homogeneity of the sample. A further evaluation of the instrument on a larger Chinese sample is warranted to support our findings.
Validating an instrument is an ongoing process and requires a wide and diverse body of evidence [
64]. To accumulate evidence on the construct validity of the questionnaire, future research is needed to examine the internal structure of the KDQOL-36™ by exploratory and confirmatory factor analysis, and to investigate the relationships of the KDQOL-36™ subscales with other external variables using different hypotheses and approaches.
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Competing interests
The authors declare that they have no conflicts of interest to disclose.
Authors’ contributions
TXJ, SC conceptualized and designed the study. TXJ performed the data collection, data entry and analyzed the data. TXJ and SC wrote the manuscript. All authors read and approved the final manuscript.