Costs and quality of life of patients with ankylosing spondylitis in Canada.

OBJECTIVE: The use of biological agents in the treatment of ankylosing spondylitis (AS) has emphasized the need for information about the current burden of the disease to estimate the cost-effectiveness of these drugs. We investigated resource utilization and utility of patients with AS in Canada.
METHODS: A cross-sectional retrospective observational study was performed in a cohort of 545 patients with AS in Alberta, Ontario, British Columbia, and Manitoba. Patients completed a questionnaire asking about their healthcare consumption, out of pocket expenses, work capacity, and need for informal care during the past 3 months. Patients' current functional status and disease activity level was assessed using the Bath AS functional and disease activity indexes (BASFI and BASDAI), and utility was determined using the EQ-5D 5-dimensional health status classification. Descriptive analysis was performed to estimate costs and utility for the sample and by level of disease severity.
RESULTS: Patients' mean age was 49.6 years and the mean disease duration was 22.3 years; 64% were male, and 63% of patients in the sample were working. The mean BASDAI score was 4.3 and BASFI 3.6, although 13% of patients in the sample had a BASFI score > or = 7. The mean annual cost per patient is estimated at 9,008 Canadian dollars (SD 17,724 Canadian dollars), and direct healthcare represented 28.9% of these costs. Patients' out of pocket costs represented 33.1%, and lost work capacity accounted for 38%. Costs increased significantly with diminishing physical function and high disease activity, covering a range of 4,000 Canadian dollars to 30,000 Canadian dollars per patient and year. The estimated cost-increase per unit-increase in the BASFI score at values < 5 was around 1,000 Canadian dollars, and more than 5,000 Canadian dollars at values > 7. The mean utility was 0.65 (SD 0.23). Utility was significantly correlated with age, sex, BASFI, and BASDAI, covering a range from 0.87 for patients with BASFI/BASDAI < or = 2 to 0.20 for patients with BASFI/BASDAI > or = 8. On average, utility decreased by 0.075 for each unit-increase in the BASFI.
CONCLUSION: All types of costs accelerate steeply with increasing loss of function (BASFI) and disease activity (BASDAI) in patients with AS, while utility decreases significantly. Treatments that control disease activity and maintain patients' function are likely to offset the high cost and low quality of life of severe disease. Our findings provide information on the burden of AS and a baseline for assessing the cost-effectiveness of the new biological agents in this indication.