Use of the Stanford Health Assessment Questionnaire in estimation of long-term productivity costs in patients with recent-onset rheumatoid arthritis

Objective: To evaluate the utility of the Stanford Health Assessment Questionnaire (HAQ) in the estimation of loss of productivity due to early rheumatoid arthritis (RA) and to develop a simple model for analysis of the cost-benefit of therapies. Methods: In the Finnish Rheumatoid Arthritis Combination Therapy (FIN-RACo) trial, 162 patients with recent-onset RA who were available for the workforce were randomized to receive either a combination of three disease-modifying anti-rheumatic drugs (DMARDs) or a single DMARD for 2 years and were followed up for 5 years. No biological drugs were used. Data on sick leave and RA-related disability pensions came from official register records. Loss of productivity was computed by both the human capital approach (HCA) and the friction cost approach (FCA). Functional capacity was assessed by the HAQ at baseline and at 6 months. Results: Over 5 years, mean loss of productivity per year was EUR 8344 by the HCA and EUR 1928 by the FCA. The level of the HAQ index at 6 months, but not the change in HAQ from baseline, determined productivity costs. With the HCA, a monotonous association between annual loss of productivity and the 6-month HAQ was found: EUR 2087 [95% confidence interval (CI) 1340-2903] per one step (0.13) on the HAQ scale from 0 to 1.88. With the FCA, the increase in loss of productivity was cut at the HAQ level of 0.5 to 0.75 (EUR 17 740 in 5 years). Conclusion: The HAQ index at 6 months may serve as a determinant of long-term RA-related indirect costs in economic analyses in early RA.