Reliability, validity and discriminatory ability of Spitzer's QL-index in dialysis patients

Quality of life outcome (QOL) on dialysis is important. We determined the measurement properties of Spitzer's QL-index, a QOL measure, in our patients on chronic haemodialysis. The QL-index measures 5 dimensions of QOL (activity, daily activities, general health, social support and psychological outlook). 59 haemodialysis (HD) patients from 2 centres were rated by 5 raters. Inter-rater agreement for the total score was good with a mean intra-class correlation coefficient 0.66 (range 0.47-0.81). That for dimension scores however was poor (weighted kappa range 0.07-1). Systematic differences between raters were also observed. Intra-rater agreement was generally better than inter-rater agreement. Significant gradients in scores were observed by age, serum albumin, comorbid disorders, previous hospitalisation, capacity for self care HD and rehabilitation status thus providing evidence for construct validity. The distribution of total scores was skewed indicating poor discriminatory ability. Nevertheless, QL-index has acceptable measurement properties for application in dialysis patients.