BACKGROUND

Health-related quality of life (QOL) assumes an increasing importance as a marker of treatment quality in many chronic diseases. Its evaluation allows the quantification of the diseases consequences according to the patient’s subjective perception and enables adjustment of  medical decisions to their physical, emotional and social needs. It also improves the adhesion to the therapeutic plan, the quality of the health care provided and the patient survival.

The multiple limitations and complications of patients in advanced stages of chronic kidney disease (CKD) or under renal substitution treatment can contribute to this QOL impairment1.

Diverse psychometric tests have been designed and validated to evaluate health-related QOL. Our purpose in this study was to evaluate the health-related QOL in four groups of CKD patients (CKD stages 1-4, kidney recipients, haemodialysis and peritoneal dialysis patients), using validated and applicable instruments.

POPULATION AND METHODS

Thirty of the 821 CKD patients stages 1-4 (CKD 1-4) and 30 of the 117 transplanted patients followed at our Nephrology Department were randomly selected. Patients at our Haemodialysis Unit (37/43) and Peritoneal Dialysis Unit (14/17) with the capacity of answering to the questionnaires were also admitted in the study.

The instruments applied were the SF-36 (Medical Outcomes Study Short-Form 36) and KDQOL-SF 1.3 (Kidney Disease and Quality of Life Short-Form).

The SF-36 is a generic questionnaire translated in more than 40 languages and already validated in Portugal2-5. It consists of 36 items grouped in eight scales that evaluate different areas of health: Physical Functioning, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional and Mental Health. These scales are grouped in two summary measures: Physical Health and Mental Health. This instrument was applied in the CKD stages 1-4 and kidney transplanted patients (KT).

KDQOL-SF 1.3 is a questionnaire that includes not only the SF-36 scales but also specific dimensions of chronic kidney disease. This dimensions include 43 items that can be summarized in 12 scales: Symptom/problem list, Effects of kidney disease, Burden of kidney disease, Work status, Cognitive function, Quality of social interaction, Sexual function, Sleep, Social support, Dialysis staff encouragement, Overall health and Patient satisfaction. It’s a reproducible questionnaire that was validated by the KDQOL Working Group studies6. It was applied in our study to haemodialysis (HD) and peritoneal dialysis (PD) patients.

The two cited instruments have punctuation from zero to 100, directly related with the QOL. In resume, higher punctuations relate to better quality of life. Our data was analyzed in a program produced by the KDQOL Working Group (www.gim.med.ucla.edu/kdqol/). The remaining statistical analysis was performed with the program Statistical Package of Social Sciences (SPSS 18.0). The quantitative variables were expressed as mean ± standard deviation and qualitative variables as absolute  numbers and percentages. We studied the association between the groups in qualitative variables by chi-square test or the contingency coefficient, as appropriate. For the quantitative variables, after checking normality with the Kolmogorov-Smirnov test, the T-Student test or Mann-Whitney were used for two groups and the table ANOVA or Kruskal-Wallis for the four groups, as appropriate. Finally, we performed a multivariate linear regression analysis in each of the groups for those variables significant in the univariate analysis or clinically relevant.

RESULTS

The peritoneal dialysis patients were younger than the other patients (38.9 ± 13.3 years in PD, 51.8 ± 10.8 years in transplanted patients, 62.2 ± 18.3 years in CKD 1-4, 67.3 ± 14.9 years in HD; p <0.001). There was no gender predominance in the four groups (43.3% of men in CKD, 50.0% in KT, 56.8% in HD and 57.1% in PD, p = 0.702) (Table 1). The mean time on dialysis was not significantly different in haemodialysis and peritoneal dialysis patients (6.1 ± 6.5 vs 1.9 ± 1.3 years, p = 0.40). The mean time after kidney transplantation was 8.7 ± 5.4 years.

The majority of haemodialysis patients were treated with on-line hemodiafiltration (56.8%) and all patients in peritoneal dialysis, except one, were in automatic peritoneal dialysis.

Twenty three patients were diabetic (20.7%), but the prevalence of diabetes was not different between the groups (p = 0.175). On the other hand, the prevalence of heart failure was tendencially higher in the haemodialysis group (HD: 40.5%; CKD: 23.3%; PD: 14.3%; KT: 13.3%; p = 0.050).

The dialysis dose was adequate in the two groups under dialytic treatment (HD: spKt/V = 2.08 ± 0.54; PD: weekly urea Kt/V = 2.25 ± 0.48 and weekly creatinine clearance = 85 ± 30 L/1.73 m2/week). The creatinine clearance was 59.3 ± 34.6 ml/min/1.73 m2 in CKD 1-4 and 74.5 ± 42.5 ml/min/1.73 m2 in the transplanted patients (p = 0.132).

All patients presented a similar albuminemia level (CKD: 3.71 ± 0.40 g/dl, KT: 3.56 ± 0.46 g/dl, HD: 3.36 ± 0.44 g/dl, PD: 3.35 ± 0.33; p = 0.231). The mean haemoglobin level of the CKD 1-4 (13.2 ± 1.7 g/dl) and transplanted patients (13.1 ± 1.9 g/dl) was higher than that of the haemodialysis (11.9 ± 1.2 g/dl) and peritoneal dialysis patients (11.5 ± 1.8 g/dl, p <0.001). The majority of haemodialysis (81.1%) and peritoneal dialysis patients (64.3%) were treated with recombinant erythropoietin (EPO). In contrast, only 23.3% of CKD patients and 16.7% of transplanted patients were under that treatment.

The best results of the SF-36 in the four groups were found in the «Social Functioning» scale of the Mental Health Component (PD: 77.68 ± 18.46; KT: 74.17 ± 29.53; CKD: 66.81 ± 31.39; HD: 62.16 ± 32.84; p = 0.192) (Table 2). The worst results were related to the «General Health» scale of the Physical Health Component (CKD: 39.92 ± 19.12; HD: 45.95 ± 21.56; KT: 47.13 ± 23.15; PD: 51.79 ± 18.89; p = 0.321).

Peritoneal dialysis patients accomplished better results in the Physical Health Component (PD: 44.90 ± 5.55; KT: 41.88 ± 10.45; CKD: 38.34 ± 10.30; HD: 5.89 ± 9.04; p = 0.016). They achieved the best results of this component in the following scales: «Physical Functioning» (PD: 68.32 ± 20.09; KT: 59.67 ± 27.85; CKD: 46.39 ± 32.73; HD: 31.89 ± 23.99; p <0.001) and «Bodily Pain» (PD: 75.54 ± 19.84; KT: 67.58 ± 27.69; HD: 57.63 ± 28.49; CKD 50.67 ± 28.36; p = 0.018). All scales of the Mental Health Component had similar punctuations in the four groups of patients (p = NS).

The second item of the SF-36 questionnaire, that compares health in general relatively to the previous year, was evaluated separately taking in consideration that is not included in the final score. This item is punctuated from one to five according to the patient’s answer: 1, much better; 2, a little better; 3, almost the same; 4, a little worse; 5, much worse. The peritoneal dialysis patients were the only ones to indicate an improvement in their health relatively to the previous year (CKD: 3.0 ± 1.1; KT: 3.0 ± 1.1; HD: 2.9 ± 1.0; PD: 2.1 ± 0.8; p <0.05).

In the kidney disease specific dimensions of the KDQOL-SF 1.3 (Table 3), the peritoneal dialysis patients had better results comparing to haemodialysis patients in the following scales: «Effects of kidney disease» (73.83 ± 17.89 vs 59.38 ± 18.76; p = 0.019), «Burden of kidney disease» (58.65 ± 27.31 vs 26.35 ± 18.58; p <0.001), «Work status» (50.00 ± 44.72 vs 19.85 ± 9.46; p = 0.001), «Overall Health» (76.67 ± 19.69 vs 46.49 ± 22.51; p = 0.021) and «Patient satisfaction» (84.72 ± 20.67 vs 70.02 ± 20.43; p <0.001). In the remaining scales, values were similar for both groups.

After adjustment in multivariate linear regression analysis for variables like age, gender, heart failure, time on dialysis, haemoglobin level and creatinine clearance, the scales that remained unchanged were «Effects of kidney disease», «Burden of kidney disease» and «Patient satisfaction» of the KDQOL-SF 1.3. Age, gender and haemoglobin level were the variables associated with the remaining scales that presented different results between groups in univariate analysis («Physical Health Component», «Physical functioning», «Bodily pain», «Work status» and «Overall health») (Table 4). Age was inversely related to the punctuation and haemoglobin level presented a direct relation with higher scores. Male patients of the CKD 1-4 group presented worst results than females in the «Bodily pain» scale (p = 0.039). 

Finally, we evaluated the association between the Mental Health Component and the treatment with antidepressants. The patients under antidepressant treatment (four patients with CKD stages 1-4, three transplanted patients, seven haemodialysis patients and one patient in peritoneal dialysis) had worst results in the Mental Health Component when compared with the remaining patients, not treated with antidepressants (36.62 ± 10.96 vs 44.17 ± 12.03; p <0.05).

DISCUSSION

The two summary measures of the SF-36 allow a fast evaluation of the health-related QOL, with scarce loss of information when the eight scales are resumed in the two main components, Physical and Mental7,8.

Several studies have already compared the QOL of dialysis patients with the general population, the majority disclosing the negative impact of chronic kidney disease and its treatments9-14. Those results are however, not confirmed in other series15,16. In our view, the present study, even with the limitation of being an observational cross-sectional study with a small number of patients, has the particularity of evaluating the health-related QOL in four groups of patients with CKD in various phases and under different renal replacement treatments (HD, PD and kidney transplant).

The worst results were registered in the scale «General Health» of the Physical Health Component. In other type of diseases, a greater impact in Physical Health comparing to Mental Health was also found17. This situation can be explained by the psychological adaptation of the sick person to the chronic illness, with a declining repercussion of the disease in its Mental Health. In our study, Physical Health was better in peritoneal dialysis patients but these differences disappeared after adjustment to confounding factors such as age and gender. Curiously, the transplanted patients didn´t achieve better results in any scale of the Physical or Mental Health Components, although these patients proved previously in other studies to have a better QOL comparing to dialysis patients18,19. Transplanted patients received their new kidney 8.7 years ago, which implied a gradual adaptation and possibly the disappearance of the health improvement feeling relatively to the pre-transplantation period.

Comparisons of QOL between haemodialysis and peritoneal dialysis patients are not consensual20,21. In our study, the PD group achieved better scores in scales like «Effects of kidney disease», «Burden of kidney disease» and «Patient satisfaction» and these results were maintained after adjustment for confounding factors. Our young peritoneal dialysis patients selected this dialytic technique to keep their active lives and the possibility to study or work. So, they are a more autonomous and motivated group. On the other hand, our haemodialysis patients are integrated in a Hospital Unit that selects older, sicker and more dependent persons. These facts may be a partial explanation for the better results of our PD patients. Another factor that may contribute for the lesser effect of the kidney disease in the QOL and better patient satisfaction may be the continuous treatment of uremia in PD. Individual characteristics of personality are obviously not evaluated in our study, but must also be considered when analysing these results.

Variables like age, gender and haemoglobin level were related with scales like «Physical Health Component», «Physical functioning», «Bodily pain», «Overall health» and «Work status». Although our PD patients had haemoglobin levels adequately corrected according to international guidelines, this modifiable factor was associated with worst results in «Work status». Taking in consideration that this specific group of patients was young and more active, the anemia correction for higher haemoglobin levels may help improve their QOL.

CONCLUSIONS

Health related QOL was better in peritoneal dialysis patients comparing to haemodialysis patients in scales such as «Effects of kidney disease», «Burden of kidney disease» and «Patient satisfaction». The worst results in the four groups were found in the Physical Health Component. Variables found to be related with QOL were age, gender and haemoglobin level. Patients under antidepressant treatment had worst results in the Mental Health Component.

The adaptation to a chronic illness is a physical, psychological and social process. The attention of the health team to the patient’s subjective perception about his state of health can be determinant in achieving the best medical intervention and improving survival.

Table 1. Demographic and clinical characteristics

Table 2. SF-36 results

Table 3. Results of KDQOL-SF 1.3 (specific scales of kidney disease)

Table 4. Significant results of the linear regression model after adjustment for age, gender and haemoglobin level (Hb)