The Prevalence and Characterization of Axial Spondyloarthritis Among Veterans with Inflammatory Bowel Disease

Background: Axial spondyloarthritis (axSpA) includes ankylosing spondylitis and inflammatory spinal disease. We validated an algorithm to identify patients with axSpA and examine the prevalence of axSpA in inflammatory bowel disease (IBD) patients. Methods: Diagnostic code algorithms to identify patients with axSpA were compared using a sample of randomly selected patients for chart review and used to estimate prevalence in a national cohort of IBD patients. Results: Using the best performing algorithm for axSpA among IBD patients [>3 codes and >90 days between encounters (positive predictive value = 0.813, negative predictive value = 0.742)], 1545 cases of axSpA were identified among 77,824 IBD patients, a prevalence of 1.99%. Fiftyfive percent of patients were diagnosed with IBD before axSpA, 24% were diagnosed concurrently, and 21% of patients were diagnosed with axSpA before IBD.