HLA-B and anterior uveitis: The target population is adults (≥18 years of age) with suspected axSpA with symptom onset at age ≤ 45, back pain ≥ 3 months, diagnosed with anterior uveitis (AU) and/or psoriasis and/or inflammatory bowel disease (IBD) and/or HLA-B 27 positive, and/or imaging suspicious for axSpA.