Rheumatoid factor is an immunoglobulin with antigenic specificity for the Fc fragment of human IgG. Detection and quantitation of RF is clinically useful due to their presence in many rheumatic and chronic inflammatory diseases.
Rheumatoid arthritis usually produces the highest titers but systemic lupus erythematosus, polyarthritis, and other chronic inflammatory diseases also produce significant RF. The majority of patients with juvenile rheumatoid arthritis (JRA) are RF negative. However, a positive RF may provide prognostic information in a JRA patient with polyarticular disease, as these children are more likely to develop severe chronic arthritis.
Our laboratory uses latex agglutination, one of the most widely used methods to detect RF. Serum containing RF will cause agglutination of latex particles that have been coated with human gamma globulins.
Titration of positives provides semi-quantitative results. Positive samples are reported as the highest titer exhibiting RF activity.