Abstract
Rheumatoid Arthritis (RA) is the most common auto-immune, chronic inflammatory joint disease. Predominantly a musculoskeletal condition with a wide spectrum of skeletal and extra-skeletal manifestations, RA has a significant footfall in orthopaedic clinical practice worldwide. RA is essentially a clinical diagnosis; however, laboratory and radiographic investigations can provide complementary diagnostic and prognostic information about the disease. Early diagnosis and initiation of appropriate management are crucial since RA patients can develop chronic, erosive arthritis if left untreated or if treatment is delayed. Rheumatoid Factor (RF) antibody test is routinely employed for diagnostic purposes in patients with suspected RA. However, RF is present only in 70%-80% of patients with RA and can be non-specific. Therefore, Anti-cyclic citrullinated peptide antibody (ACPA), a novel immunological marker for RA is increasingly being utilised to provide higher specificity and a better prognostic indicator in RA patients. We describe the immunological basis of ACPA test and highlight its current applications in the diagnosis, prognosis and monitoring of RA in clinical practice.