CRP and rheumatoid arthritis: In RA patients, midkine levels in serum or synovial fluid were elevated [13, 15], and its levels were positively correlated with IL-17 and C-reactive protein (CRP), but not with Disease Activity Score (DAS), rheumatoid factor, erythrocyte sedimentation rate (ESR), anti-keratin antibodies and anti-cyclic citrullinated peptide antibodies [21].