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Rheumatoid Factor
Aka: Rheumatoid Factor, RF, Rheumatoid Factor Test
- See Also
- Rheumatoid Arthritis
- Anticyclic Citrullinated Peptide Antibody
- Mechanism
- Polyclonal B Cell activation synthesizes RF autoantibody
- RF IgM (rarely IgG) Antibody
- Binds IgG constant region (crystallizable fragment)
- Serum Detection
- Latex fixation
- Agglutination of latex particles
- Latex coated with human IgG
- Sheep Cell Agglutination assay indications
- Negative latex fixation despite high suspicion
- Causes: Negative
- Normal
- Conditions in which Rheumatoid Factor is expected to be negative
- Osteoarthritis
- Ankylosing Spondylitis
- Gout
- Chondrocalcinosis
- Suppurative Arthritis
- Psoriatic Arthritis
- Enteropathic Arthritis
- Reiter's Syndrome
- Causes: Positive
- Rheumatoid Factor present in normal persons
- Very Low titers (<1:80) present in many patients
- Normally present in 1-5% of general population
- Incidence of RF increases with age
- Incidence of RF increases in age over 65 years: 10%
- Rheumatoid Arthritis (33-90%)
- RF Titer alone does not diagnose Rheumatoid Arthritis
- Test Sensitivity: 69%
- Test Specificity: 85%
- Positive Likelihood Ratio (LR+): 4.86
- Negative Likelihood Ratio (LR-): 0.38
- Prognosis worse with high titer at onset
- Higher titers are associated with erosive Arthritis, extraarticular involvement
- RF Incidence increases with duration of disease
- Three months: 33%
- Six months: 45%
- One year: 75%
- Eighteen months: 90%
- Up to 20% of RA patients remain seronegative
- Other Autoimmune Disease
- Sjogren's Syndrome (75 to 95%)
- Systemic Lupus Erythematosus (15 to 35%)
- Scleroderma (20 to 30%)
- Polymyositis or Dermatomyositis (10%)
- Cryoglobulinemia (40 to 100%)
- Mixed Connective Tissue Disease (50 to 60%)
- Infections
- Bacterial Endocarditis
- Osteomyelitis
- Tuberculosis
- Syphilis
- Hepatitis (Acute and Chronic)
- Mononucleosis
- Parasitic Infection
- Viral infection (esp. Mumps, Rubella, Influenza)
- Lung Disease
- Asbestosis
- Diffuse interstitial pulmonary fibrosis
- Sarcoidosis
- Silicosis
- Gastrointestinal Conditions
- Hepatic Cirrhosis
- Primary biliary Cirrhosis
- Cancer
- Leukemia
- Colon Cancer
- References
- Ali (2018) Am Fam Physician 98(3): 164-70 [PubMed]
- Shmerling (1991) Am J Med 91:528-34 [PubMed]
- Nishimura (2007) Ann Intern Med 146(11): &97-808 [PubMed]