What is a rheumatoid factor (RF)?
Rheumatoid factors are antibodies directed against the Fc region of IgG.
What percentage of patients with rheumatoid arthritis have a positive RF?
Only about 60% of patients with rheumatoid arthritis test positive for RF. The presence of a RF provides information about prognosis and disease severity, but not disease activity. Those with high titre RF are at greater risk for a severe disease course and for extra-articular manifestations.
List 4 other diseases that are associated with a positive RF.
Other conditions associated with a positive RF include:
- Sjogren’s syndrome
- mixed connective tissue disease
- systemic lupus erythematosus
- liver disease
- lung fibrosis
- older age.