The present cohort study demonstrated that KT patients had higher SF-36 scores with respect to both physical and mental QOL than CKD patients at the same CKD stage; however, they had similar CKD-targeted scores compared to CKD patients with similar renal function. KT was a significant prognostic factor associated with better QOL, independent of renal function.
CKD patients suffer from a low QOL 1,2. The AUSDiab analysis reported that physical QOL in CKD patients decreased in parallel with eGFR decline during a 5-year follow-up 29. Consistently, our study showed that SF-36 scores, mainly PCS scores decreased over 5 years. The CKD-targeted score also decreased along with decreasing renal function, and better renal function was independently associated with higher CKD-targeted QOL, in line with previous studies 7,12,29. A Korean community-based analysis also showed that QOL was inversely correlated with CKD stage 30. Taken together, these findings clearly demonstrate that QOL in CKD patients becomes worse along with decreasing renal function, which is an important prognostic factor associated with QOL in CKD patients.
KT immediately improves the renal function of ESRD patients. A Greek study demonstrated improvement in QOL components such as better general health perception, role of emotional function, and vitality among the subdomains of the SF-36 score in KT patients 1 year after transplantation 31. A recent US study reported deterioration of physical QOL and a stationary CKD-targeted score at 1 month after KT, but significant improvements in physical and CKD-targeted QOL at 3 months, especially for more frail patients 32. We also previously reported significant improvements in HRQOL for both SF-36 and CKD-targeted QOL scores at 2 years after KT 33. Furthermore, the present follow-up study of a larger group demonstrated that the improved QOL at 2 years after KT began to decline at 4-year follow-up in the KT group.
Previous studies have assessed the association between QOL at the early phase with long-term clinical outcomes such as mortality and allograft function in KT populations. Higher physical and mental health scores are significant prognostic factors for better 10-year survival 34, and lower physical function and general health perception in the physical component are independent risk factors for 7-year mortality 19. We hope that further long-term follow-up studies using our KT cohort can demonstrate the impact of QOL at each time-point and its influence on the long-term clinical outcomes after KT.
We investigated the prognostic factors associated with QOL in KT and CKD cohorts. A single-center study in Thailand reported that gender, marital status, higher income, and higher education were associated with increased QOL after KT 35. In the present study, absence of diabetes mellitus, higher blood hemoglobin level, higher monthly income, marriage, and employment were independently associated with higher SF-36 scores in KT or CKD patients. The CKD-targeted score was significantly associated with decreased renal function, absence of diabetes, higher income, employment, and married status in both the KT and CKD groups. The hemoglobin level consistently influenced QOL in KT and CKD patients 36–38. Diabetes was another important prognostic factor influencing QOL in the present KT population in parallel with reports of non-KT populations 39. These findings suggest that efforts are needed to improve QOL during the pre-KT CKD phase to achieve a better post-KT QOL along with correction of anemia.
Because KT patients remain in a state of CKD, we tried to explore differences in QOL between KT and non-KT CKD patients with similar renal function. Previous studies demonstrated that KT patients had better QOL than ESRD patients undergoing dialysis 17,40−43. The overall improvement in QOL after KT was mostly attributed to improvement of physical function 44. However, few studies have compared QOL between KT patients and pre-dialysis CKD patients. A small-sized, single-center study that compared 38 stable KT recipients and 38 CKD patients at CKD stage 3b‒4 showed no significant difference in the SF-36 QOL score, but a better QOL in non-dialysis CKD patients than in KT patients based on a visual analogue scale 45. In contrast, in the present multicenter study, KT patients had higher SF-36 QOL scores than the CKD patients after adjustment for other factors, including renal function. These positive effects of KT on QOL were observed in various domains of the MCS and in the general health domain of the PCS. When we analyzed the impact of KT on QOL over time compared to CKD according to CKD stages, SF-36 scores were higher in KT patients than in CKD patients at CKD stage 3 as well as CKD stages 1‒2. On the other hand, CKD-targeted scores in KT and CKD patients did not differ at baseline and there was no significant difference in the change of CKD-targeted scores over time between the two groups irrespective of CKD stage. Interestingly, the difference in both SF-36 and CKD-targeted scores between the two groups increased over time at CKD stage 3, suggesting that the beneficial effects of KT on HRQOL compared to CKD might increase with CKD progression. Overall, KT patients had better SF-36 scores than CKD patients independent of renal function, whereas the CKD-targeted score was mainly dependent on renal function and KT did not provide additional benefits in patients with similar renal function.
The reasons why KT patients have better QOL than CKD patients with similar renal function are unclear. KT patients might interpret their QOL more positively than CKD patients, which may be related to their history of improvement with KT and lower levels of concern about future prognosis compared to CKD patients without a dramatic recovery experience. Indeed, depression was found to be the most important factor influencing HRQOL in the CKD population.46 Depressive mood consists of lack of enthusiasm, feelings of hopelessness for the future, feeling left behind in society, and an associated feeling of worthlessness, which may result in a poor QOL at advanced CKD stages. In contrast, the KT population considered the possibility of recovering renal function with treatment or retransplantation, which might bring hope and reduce depressive mood. The higher QOL in KT patients might allay fears related to disease progression so as to conform to the CKD status.
This study had a few limitations. First, the number of patients at the 4-year follow-up was relatively small in the KT population. However, the second set analysis of the patients with the QOL data at both baseline and the 4-year follow-up showed similar trends to the main analysis (data not shown). Second, this study did not include advanced CKD stage 4‒5 patients because of low numbers, so we could not compare KT and CKD patients at this advanced stage. Therefore, further longer-term follow-up studies using this cohort could help to more adequately assess the association between renal functional deterioration and QOL changes in KT patients, and the impact of KT on QOL compared to CKD in advanced CKD stages. Third, unfortunately the follow-up time-points of serial QOL assessment were different in the KT and CKD cohorts. Future comparative studies with the same follow-up schedule are needed to confirm our findings.
Despite these limitations, to the best of our knowledge, this prospective, longitudinal HRQOL study represents the longest follow-up QOL assessment of KT patients at multiple time-points. Furthermore, this is the first study to compare QOL between KT and CKD patients with similar renal function and a mild to moderate degree of CKD (stage 1‒3). Based on this study, further studies using other cohorts could confirm our findings.
In conclusion, KT patients have better QOL than CKD patients with similar renal function at CKD stages 1–3. Therefore, improvement in QOL is an important benefit of KT for CKD patients.