Validation of the English Version of the Kidney Disease Quality of Life Questionnaire (KDQOL-36) in Haemodialysis Patients in Singapore

Background To validate a widely used health outcomes instrument for patients with chronic kidney disease and on dialysis, the Kidney Disease Quality of Life questionnaire (KDQOL-36), in English-speaking haemodialysis patients in Singapore. Methods This study is a secondary data analysis using the KDQOL-SF (version 1.3) data collected from a cross-sectional survey of haemodialysis patients in Singapore. Cronbach's alpha was used to test internal consistency reliability. Multi-item scales were assessed using item-to-scale correlation and factor analysis. Both confirmatory and exploratory factor analyses were performed separately for generic and disease-targeted scales. Construct validity was assessed by correlation between disease-targeted and generic scales. Criterion validity was assessed by correlation of the physical component summary (PCS-12) and mental component summary (MCS-12) from KDQOL-36 with the corresponding PCS-36 and MCS-36 from the KDQOL-SF. Results Three hundred ninety-four patients who completed the interviews in English [male 55.8 %, mean age (SD) 52.4 (11.7) years] were involved. Kidney disease scales exhibited desirable internal consistency (Cronbach's alpha 0.822-0.906) and item-to-scale correlation (range 0.763-0.903), and a three-factor model fit the data well [comparative fit index (CFI) 0.934, root mean square error of approximation (RMSEA) 0.085]. For the generic Short Form 12 Health Survey (SF-12) items, a two-factor model (physical and mental) showed poor overall fit, but a three-factor structure (role, physical and mental functions) achieved good model fit (CFI 0.999, RMSEA 0.027). Correlation between disease-targeted and generic scales was weak to moderate (range 0.286-0.418). Correlation between SF-12 and SF-36 was 0.750 for PCS and 0.797 for MCS. Conclusion The English version of the KDQOL-36 appears to be reliable and valid to measure quality of life for haemodialysis patients in Singapore.