Background Many patients with rheumatoid arthritis (RA) have several chronic co-occuring disorders (comorbidities). There is an inverse relationship between comorbidy and health-related quality of life (HRQoL). Because indirect utility measurement involves HRQoL, comorbidities probably affect utility assessment.
Objectives We investigated the impact of comorbidities on the measure of utility with 2 indirect utility measures widely used to calculate quality-adjusted life-years (QALYs), SF-6D and EQ-5D, in patients with rheumatoid arthritis (RA).
Methods 962 patients of COMEDRA, a French multicentric clinical trial involving patients with stable RA, were included in the study. Comorbidities assessed were chronic obstructive pulmonary disease, diabetes, hypertension, obesity, cardio-vascular diseases, stroke, hypercholesterolemia, renal insufficiency and osteoporosis. Bio-clinical variables were also recorded (activity by DAS28, function by HAQ score, Rheumatoid Arthritis Impact of Disease score ...).
Two separate linear regression models, using the number of comorbidities and the different categories of comorbidities, were fitted to determine predictors of utility scores.
Results For the 962 patients included (mean age ± SD =57.7±11.1 years, 79% women), the mean SF-6D utility score was 0.67±0.12 (range: 0.357, 1), and the mean EQ-5D utility score was 0.64±0.27 (range: -0.416, 1). The mean number of comorbidities was 1.02±0.95 and 40.6% of patients have 1 comorbidity, 19.3%, 2 comorbidities and 7%, ≥3 comorbidities. In the first multivariate model, for each additional comorbidity (range 0–5) the mean SF-6D utility score decreased of 0.007 point (p<0.0001) and the mean EQ-5D utility score decreased of 0.028 point (p<0.0001). In the second model, including comorbidities by categories, no comorbidity predicted significantly low utility score. In both regression models a worsened function (increased HAQ score) significantly decreased the EQ-5D utility score and a worsened mental state (increased mental component of RAID score) significantly decreased the SF-6D utility score. The number of comorbidities explained <1% of the variance in utility scores (partial R-square=0.0097 for EQ-5D and 0.003 for SF-6D), whereas the HAQ score explained 51.2% of the variance in EQ-5D utility score in both models and the mental state explained 38,2% of the variance in SF-6D utility score.
Conclusions Compared to greater negative effect of functional impairment for EQ-5D and mental state for SF-6D, the number of comorbidities has a negative but relatively marginal impact on indirect utility scores in RA.
Disclosure of Interest : None declared