To evaluate the prevalence, types, and out-patient direct medical costs of comorbid conditions in patients with RA in Thailand.

Information of the patients with RA treated by rheumatologists with at least one disease modifying antirheumatic drugs (DMARDs), including demographic data, RA-related medication types and treatment costs, comorbidity-related medication types and treatment costs, and total direct medical costs, was captured from King Chulalongkorn Memorial Hospital databases.

The data from 684 patients with RA were included for analysis. The majority of the patients were prescribed combined DMARDs, while only 2.5% received biologics. Comorbid conditions were reported in 434 patients (63.5%). The most common comorbid condition was hypertension (51.2%). Advanced age and presence of healthcare coverage was associated with comorbid conditions. The average annual cost of non-RA-related treatments in patients with comorbid diseases was 15 times the cost in those without comorbidities (1546 vs. 104USD; P<0.001) while the total direct medical cost in patients with comorbid conditions was twice that in patients without comorbid diseases (4118 vs. 2045USD; P<0.001). Parameters that influenced total direct medical costs were RA medications costs, comorbidity, healthcare coverage, patient's age, and types of DMARDs.

Comorbid conditions were common in this study. However, the major cost component incurred in RA patients was the costs of RA medications and services, while the out-patient costs of comorbid conditions accounted for approximately 38% of the total costs.