Figure 1: Flowchart depicting the inclusion/ exclusion of study subjects to the study. Patients in this study were included from the “Spines of Southern Denmark” cohort from the spine Center of Southern Denmark. Patients with low back pain (LBP) >3 month and a “positive MRI” or positive HLA-B27 with one or more concomittant SpA feature(s) were referred to a rheumatologist. Patients were grouped with axial spondyloarthritis (axSpA) according to ASAS criteria for axSpA (n=96), patients not fully meeting the ASAS criteria with either MRI sacroilitis or positive HLA-B27 with only one concomittant SpA feature (non-axSpA, n=38) and patients with non-specific LBP without relation to SpA (n=82). As a control group, blood donors (BD) were included from the local blodd bank (n=40).