Method for detecting rheumatoid arthritis employing the CB10 peptide of mammalian type II collagen as an antigen

A predictive test for rheumatoid arthritis comprises the detection of antibodies to collagen in a biological sample from a patient by contacting the biological sample with an antigen comprising the CB10 peptide of mammalian type II collagen, or an antibody-binding fragment or variant thereof, for a time and under conditions for an antibody-antigen complex to form, and detecting the antibody-antigen complex, for example by immunoassay. A diagnostic test kit is also disclosed.