The quality-adjusted life-year (QALY) is used to measure outcome in rheumatoid arthritis (RA) studies; identification of drivers of a gain in QALY might help predict a treatment response. We investigated how changes in components of the Disease Activity Score-28 joints (DAS28) were associated with the European League Against Rheumatism (EULAR) and European Quality of Life 5 Dimensions (EQ-5D) responses; and what baseline variables predicted the change in QALY following 1 year of biological therapy.
Data were collected at baseline and after 3, 6, and 12 months of biological therapy in Danish patients with RA and included bDAS28, sociodemographic data, comorbidity, Health Assessment Questionnaire (HAQ), and EQ-5D scored using the Danish algorithm. A cross-tabulation based on EULAR versus EQ-5D responses was performed, and the association of each DAS28 component across the EULAR/EQ-5D response groups was tested. Predictors of a change in QALY were assessed in a multiple regression model including baseline clinical and patient-reported data as explanatory variables.
In total, 315 patients entered the study; 77% were women, 78% IgM rheumatoid factor-positive, with mean age 55 (SD 13) years, disease duration 10 (SD 8) years, mean DAS28 4.9 (SD 1.2), HAQ score 1.22 (SD 0.70), and EQ-5D score 0.60 (SD 0.19). Sixty-eight percent of patients gained QALY; the mean gain was 0.14 (SD 0.13). The patient global score was strongly correlated with both EULAR and EQ-5D responses. The gain in QALY increased with increasing patient global score and number of swollen joints, but not with C-reactive protein (CRP).
The subjective patient global score was the best baseline predictor of gain in QALY following biological therapy, while the objective CRP measure had no predictive value. It seems that no sharp demarcation between objective and subjective measures could be determined.