Axial spondyloarthritis is an inflammatory disease characterized by the involvement of the sacroiliac joints and the spine. Disease activity and structural changes are determined by using physical examination, imaging studies, laboratory parameters, and patient-reported indices. Among laboratory studies, Erythrocyte sedimentation rate (ESR) and c-reactive protein (CRP) are the most commonly utilized parameters. However, the level of ESR and CRP are inadequate in demonstrating disease activity and inflammation compared to other diseases. In this study, the investigators aimed to analyze and compare the systemic inflammatory index (SII), which is a hematologic parameter between subjects with radiographic axial spondyloarthritis, non-radiographic axial spondyloarthritis, and healthy controls. Secondarily, the relationship between disease activity and enthesitis score and SII scores in patients with radiographic and non-radiographic axial spondyloarthritis will be investigated.