Background
- General class of IgM antibodies to the Fc region of IgG
- Most asymptomatic people with positive RF do not progress to rheumatoid arthritis
- Neither specific nor sensitive for RA
Differential Diagnosis
- Rheumatic disorders
- Rheumatoid arthritis (26-90%)
- Systemic lupus erythematosus (15-35%), Sjögren syndrome (75-95%), and mixed connective tissue disorder (50-60%)
- Type II and III cryoglobulinemia (40-100%)
- Polymyositis and dermatomyositis (5-10%)
- Chronic infections
- Bacterial endocarditis (25-50%)
- Hepatitis B and hepatitis C (20-75%)
- Other viruses, such as HIV, Epstein-Barr virus, and CMV
- Some parasites, including malaria, schistosomiasis, and toxoplasmosis
- Inflammatory disorders
- Cirrhosis (25%)
- Primary biliary cirrhosis (45-70%)
- Idiopathic pulmonary fibrosis (10-50%)
- Sarcoidosis (3-33%)
- Silicosis and asbestosis (30-50%)
- Malignancies
- B-cell disorders (5-25%)
- Normal aging
- ≥65 years of age (5-25%)
Further Reading
- Rheumatoid Factors: Clinical Applications. Dis Markers. 2013;35(6):727–734. doi: 10.1155/2013/726598
