quantification of rheumatoid factors, antibodies in the serum of individuals with rheumatoid arthritis that react with antigenic determinants or immunoglobulins that enhance agglutination of suspended particles coated with pooled human gamma -globulin. Rheumatoid factors also occur in other autoimmune and certain infectious diseases. The trait is Experimental Factor Ontology id EFO_0005767 (rheumatoid factor measurement).