PRTN3 and rheumatoid arthritis: While in RA patients the serum RF and ACPA levels, together with erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels, are established serum biomarkers to assess disease activity, only ESR and CRP are used as a serum biomarker in seronegative arthritic patients for appropriate patient management and treat-to-target strategy.