Anti–cyclic citrullinated peptide (anti-CCP) using a peptide of filaggrin has been used extensively as a new serologic marker of rheumatoid arthritis (RA) (1,2). Many studies have confirmed that anti-CCP enzymelinked immunosorbent assay (ELISA) is as sensitive as rheumatoid factor (RF) and much more specific for RA among various rheumatic diseases (2). However, anti- CCP in other diseases has been less well studied. Patients with certain infectious diseases, such as hepatitis C and tuberculosis (TB), can present with arthritis and frequently also have serum RF, making it difficult to distinguish infectious disease–related arthritis from RA. Thus, the utility of anti-CCP testing under these clinical circumstances is important. Studies in patients with hepatitis C viral infection.
