Patients with rheumatoid arthritis can synthesize immune proteins that bind to citrullinated peptides, and anti-citrullinated antibodies can be detected in 80-90% of rheumatoid patients, with some studies showing specificity approaching 90%. Citrullinated peptides can be produced by B cells in synovial tissue and are detected in synovial fluid. Anti-cyclic citrullinated peptide antibodies (CCP) are a type of rheumatic autoantibody system and have a good specificity for the diagnosis of early rheumatoid arthritis, the higher the index, the greater the likelihood of rheumatoid arthritis. Anti-cyclic citrullinated peptide antibody is not only an early diagnostic indicator of rheumatoid arthritis, but also a sensitive indicator to distinguish between erosive and non-erosive rheumatoid arthritis, and those who are positive usually develop or tend to develop more severe joint deformation (bone destruction) than those who are negative for the antibody. Combined testing for anti-cyclic citrullinated peptide antibodies and rheumatoid factor is more effective in predicting disease and diagnosing rheumatoid arthritis earlier. Patients with clinical manifestations or confirmed rheumatoid arthritis who are negative for rheumatoid factor but positive for anti-cyclic citrullinated peptide antibodies have rapid progression of joint destruction and poor prognosis for joint function. Elevated anti-cyclic citrullinated peptide antibodies do not mean that the disease is in an active phase.