ACPA: anti-citrullinated protein antibodies; CRP: C-reactive protein; DAS28-ESR: Disease Activity Score-28 Based on Erythrocyte Sedimentation Rate; EORA: elderly-onset rheumatoid arthritis; ESR: erythrocyte sedimentation rate; HAQ: Health Assessment Questionnaire; NA: not available; SD: standard deviation; SDAI: Simplified Disease Activity Index; YORA: young-onset rheumatoid arthritis. Here, CRP is linked to rheumatoid arthritis.