The present invention provides novel citrullinated peptides, their use in methods for aiding, assisting, improving, or facilitating the diagnosis or prognosis of rheumatic diseases such as rheumatoid arthritis (RA), and methods for identifying novel citrullinated peptides that are immunoreactive with anti-citrullinated protein antibodies (ACPAs). The present invention also provides methods for detecting rheumatoid factor (RF) using novel RF detection reagents as a means to aid, assist, improve, or facilitate the diagnosis or prognosis of rheumatic diseases such as RA. Kits comprising at least one of the novel citrullinated peptides and/or RF detection reagents of the present invention are also provided.
