Rheumatoid factor

An autoantibody (antibody that attacks healthy tissues). Elevated rheumatoid factor (low positive: 20 - 40 IU/mL, high positive: >40 IU/mL) supports the diagnosis of rheumatoid arthritis (sensitivity 75%) or other autoimmune disorders such as Sjögren's syndrome, lupus, and scleroderma. Other possible causes are viral infection (HCV, HIV), bacterial infections (tuberculosis, endocarditis), parasitic infection (malaria), malignancy (leukemia), sarcoidosis and advanced age (can appear naturally in older adults without any disease).