- SpA spondyloarthritis, ASAS Assessment of Spondyloarthritis International Society, HLA-B27 human leukocyte antigen B27, BASDAI Bath Ankylosing Spondylitis Disease Activity Index, CRP C-reactive protein, ESR erythrocyte sedimentation rate, WBC white blood cells, RBC red blood cells, MRI magnetic resonance imaging. NI not included in the multivariate analysis