Kidney Disease Quality of Life 36-Item Short Form Survey (KDQOL-36) Normative Values for the United States Dialysis Population and New Single Summary Score

Abstract

Reliable, valid, and interpretable patient-reported outcome measures for kidney patients are needed for patient monitoring and use as outcomes in clinical trials. The Kidney Disease Quality of Life 36-item short form survey (KDQOL-36) is often used with patients on dialysis, but improvements are needed to facilitate interpretability of its scores. The authors calculate normative values for the KDQOL-36 scales referenced to the United States dialysis population, which allow comparison of group means and individual scores with national averages, such as by dialysis centers when fulfilling their required annual assessment of patients’ quality of life. The authors also created the KDQOL-36 Summary Score (KSS), a composite of items from the KDQOL-36’s kidney-targeted scales, which may be useful when kidney-targeted health-related quality of life needs to be summarized in a single score. The Kidney Disease Quality of Life 36-item short form survey (KDQOL-36) is a widely used, patient-reported outcome measure for patients on dialysis. Efforts to aid interpretation are needed. We used a sample of 58,851 dialysis patients participating in the Medical Education Institute (MEI) KDQOL Complete program, and 443,947 patients from the US Renal Data System (USRDS) to develop the KDQOL-36 Summary Score (KSS) for the kidney-targeted KDQOL-36 scales (Burdens of Kidney Disease [BKD], Symptoms and Problems of Kidney Disease [SPKD], and Effects of Kidney Disease [EKD]). We also used the MEI and USRDS data to calculate normative values for the Short Form-12 Health Survey’s Physical Component Summary (PCS) and Mental Component Summary (MCS), and the KDQOL-36’s BKD, SPKD, and EKD scales for the United States dialysis population. We used confirmatory factor analysis (CFA) models for KDQOL-36 kidney-targeted items, evaluated model fit with the comparative fit index (CFI; >0.95 indicates good fit) and root-mean-squared error of approximation (RMSEA; <0.06 indicates good fit), and estimated norms by matching the joint distribution of patient characteristics in the MEI sample to those of the USRDS sample. A bifactor CFA model fit the data well (RMSEA=0.046, CFI=0.990), supporting the KSS ( α =0.91). Mean dialysis normative scores were PCS=37.8 and MCS=50.9 (scored on a T-score metric); and KSS=73.0, BKD=52.8, SPKD=79.0, and EKD=74.1 (0–100 possible scores). The KSS is a reliable summary of the KDQOL-36. The United States KDQOL-36 normative facilitate interpretation and incorporation of patient-related outcome measures into kidney disease care.