CRP and kidney disorder: The variables selected for the imputation model included registry (country), age at baseline, gender, education, disease duration, baseline disease measures, HLA-B27 status, presence/absence of comorbidities (psoriasis, uveitis, cardiovascular, diabetes, kidney disease, inflammatory bowel disease), treatment (TNFi, conventional synthetic DMARDs, NSAIDs), inflammation (CRP, ESR), baseline disease measures (Bath indices), lifestyle factors, and BASDAI50 response at 3 and 12-month follow-up.