In a 2016 survey conducted by the National Kidney Disease Council of Japan on primary diseases affecting dialysis patients,15 chronic glomerulonephritis, diabetic nephropathy, nephropathy, nephrosclerosis, cystic kidney, and pregnancy toxemia were reported in 36.0%, 32.5%, 10.2%, 4.9%, 4.9%, and 0.6% of subjects, respectively. Subjects of that study could be considered representative of the Japanese population.
When using EQ-5D-5L to compare the QOL of dialysis patients with that of healthy Japanese subjects, a survey by Shiroiwa et al.16 reported scores of 0.939, 0.899, and 0.841 in the age groups of ~ 59 years, 60–69 years, and 70 years or older, respectively, with differences of 0.134 and 0.151 in the age groups of ~ 59 and 60–69 years, respectively. The difference was smaller in the 70 years and older age group (0.062). From this comparison, it can be inferred that the disease burden of dialysis is higher in younger people.
A study that used the Kidney Disease QOL Instrument (KDQOL) to compare the disease burdens of dialysis patients in Japan, Europe, and the United States17 found that Japanese dialysis patients reported the highest physical function but also had the highest disease burden. The parameters used to assess the burden of disease, as measured using the KDQOL, included whether the subject’s kidney disease interferes with their life, takes too much of their time, makes them feel frustrated, or makes them feel like a burden on their family. This is noteworthy, although KDQOL findings cannot simply be compared with QOL measured using the EQ-5D-5L because it asks about the burden on their families. This may be associated with a lower burden of disease according to the KDQOL, but we could not confirm the evidence for this in Japan.
When compared with foreign reports that used the EQ-5D-5L, a higher percentage of respondents reported the most problems with the pain/discomfort dimension, which was similar to the results of our study.18, 19 This suggests that in dialysis patients, pain/discomfort, which is the most subjective dimension related to dialysis, may still be a significant problem. In a survey of symptoms experienced by dialysis patients, Abdel-Kader et al.20 reported that tiredness or lack of energy, worry, dry skin, itchiness, trouble staying asleep, trouble falling asleep, sadness, irritability, difficulty with sexual arousal, bone or joint pain, muscle cramps, and anxiousness, etc. were high in dialysis patients. Claxton et al.21 reported that symptoms such as bone/joint pain, sleeplessness, worry, sadness, nausea, anxiety, and nervousness were frequently observed. These common symptoms were considered to be expressed in the pain/discomfort dimension of the EQ-5D-5L. Although this study showed a decrease in the mobility dimension, many studies22–27 showed a relationship between muscle weakness and exercise capacity in hemodialysis patients, and it was considered a QOL characteristic.
According to a study by Li et al.,17 which used the EQ-5D-5L to examine the QOL of patients before kidney transplantation, the mean utility value score was 0.773, which was close to our study results and those of similar foreign reports, although there were differences in the scoring algorithms used to calculate these results. In studies by Shimizu et al.13 and Takara et al.,11 the mean scores were 0.738 and 0.76–0.71, respectively, indicating that patients with kidney disease could maintain their QOL on dialysis. Moreover, this well-maintained QOL remained unaffected by diagnosis and age. Only dialysis duration affected QOL. Prolonging the dialysis period decreased QOL. However, the reason for this remains unclear and is a subject for further studies.
This study had limitations. As this study was conducted at a single institution, whether the findings are representative of all dialysis patients in Japan is questionable. This was refuted by the fact that the disease rates in the previous national survey were similar. In addition, the dialysis patients’ symptoms, comorbidity and other demographic factors (income, job, marital status, et al.) were not included as survey items; thus, the relationships between the factors and QOL could not be clarified. Since there seems to be a causal relationship between symptoms experienced by dialysis patients and QOL assessed using the EQ-5D-5L, future studies should be used to clarify this relationship. In future, we plan to perform studies with higher numbers of cases and analyze changes in QOL over time.