Rheumatoid factor (RhF) is an autoantibody (typically an IgM) directed against the Fc portion of IgG. While RhF is most classically associated with rheumatoid arthritis (RA), its presence can be seen in several other conditions. Here are diseases and conditions where a positive RhF might be detected:
- Autoimmune Diseases:
- Rheumatoid Arthritis (RA): RhF is present in about 70-80% of patients with RA, but its absence doesn’t rule out the disease.
- Sjögren’s Syndrome: This is the second most common condition associated with a positive RhF.
- Systemic Lupus Erythematosus (SLE)
- Systemic Sclerosis (Scleroderma)
- Other Inflammatory Joint Diseases:
- Juvenile Idiopathic Arthritis (JIA): Some types of JIA can have a positive RhF.
- Adult-Onset Still’s Disease
- Infections:
- Chronic Hepatitis C Infection: A significant percentage of patients with chronic hepatitis C have a positive RhF.
- Endocarditis
- Tuberculosis
- Syphilis
- Leprosy
- Malaria
- Other Conditions:
- Chronic Lung Diseases: Such as interstitial lung disease or chronic obstructive pulmonary disease (COPD).
- Chronic Liver Diseases: Especially cirrhosis.
- Cryoglobulinemia: Particularly type II and III, which can often be seen in the context of hepatitis C infection.
- Monoclonal Gammopathies: Like Waldenström macroglobulinemia.
- Aging:
- A small percentage of elderly individuals might have a positive RhF without any associated disease.
- Healthy Population:
- A small proportion of the general healthy population can have a positive RhF without evidence of autoimmune disease.
It’s essential to understand that while RhF is used to support the diagnosis of RA and some other conditions, its presence alone does not confirm a diagnosis, given its potential presence in various other diseases and even some healthy individuals. Clinical context, physical examination, and other diagnostic tests are crucial in determining the underlying cause or significance of a positive RhF.