Short-Form 12 or Short-Form 36 to measure quality-of-life changes in dialysis patients?

Short-Form 36 (SF-36) is a self-report health-related quality-of-life (HRQOL) questionnaire, widely used in dialysis patients. It consists of physical and mental component scores (PCS/MCS), ranging from 0 to 100. To improve efficiency, the Short-Form 12 (SF-12) was developed to reproduce PCS and MCS. We assessed the ability of SF-12 versus SF-36 to detect change over time, and the association of SF-12 versus SF-36 with short-term and long-term mortality in dialysis patients.

Patients were selected from the Netherlands Cooperative Study on the Adequacy of Dialysis (N = 1379), a prospective follow-up study among incident dialysis patients (62.1% HD) who completed SF-36 measurements every 6 months. Changes in scores of SF-12 versus SF-36 were compared with intra-class correlation coefficients (ICCs). Subsequently, Bland-Altman plots were used to assess limits of agreement. Relationship with mortality was assessed with Cox models with and without a time-dependent variable, adjusted for age, sex, ethnicity, comorbidity and dialysis modality at baseline.

ICC for change in scores was 0.90 for MCS and 0.84 for PCS. Mean difference was -0.1 and 0.2, respectively, and limits of agreement were -8.3 to 8.4 for MCS change in scores and -8.8 to 9.2 for PCS. Adjusted hazard ratio's for mortality per 5 units increment were 0.87 (95% CI: 0.84-0.91) for MCS12, 0.87 (95% CI: 0.84-0.90) for MCS36, 0.79 (95% CI: 0.76-0.83) for PCS12 and 0.75 (95% CI: 0.71-0.78) for PCS36.

SF-12 can be used to detect change in HRQOL in cohort studies on dialysis patients. SF-12 and SF-36 were similarly associated with short-term and long-term mortality. However, the wide limits of agreement indicate that SF-12 and SF-36 can give different scores on the individual level, suggesting that for individual purposes SF-36 instead of SF-12 should be used.