CRP and psoriatic arthritis: Abbreviations: anti-CCP - anti-cyclic citrullinated peptide antibodies; ACR - America College of Rheumatology; CRP - C-reactive protein; CASPAR - The Classification Criteria for Psoriatic Arthritis; DMARD – disease modifying anti-rheumatic drug; EULAR - European League against Rheumatism; ELISA - enzyme-linked immunosorbent assay; ESR - erythrocyte sedimentation rate; HLA – human leukocyte antigen; PsA - psoriatic arthritis; RA - rheumatoid arthritis; RF - rheumatoid factor; ROC - receiver operating characteristic.