Rheumatoid Arthritis Factor Test
The Rheumatoid Arthritis Factor is often evaluated in patients suspected of having any form of arthritis or destructive articular disease even though positive results can be due to other causes, and negative results do not rule out disease. But, in combination with signs and symptoms, it can play a role in both diagnosis and disease prognosis. It is part of the usual disease criteria of rheumatoid arthritis.
The Rheumatoid Arthritis Factor test is often evaluated in patients suspected of having any form of arthritis or destructive articular disease, even though positive results can be due to other causes, and negative results do not rule out disease. But, in combination with signs and symptoms, it can play a role in diagnosis and disease prognosis. It is part of the usual disease criteria of rheumatoid arthritis.
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What Does The Rheumatoid Factor Detect?
The presence of rheumatoid factor in serum can also indicate suspected autoimmune activity unrelated to rheumatoid arthritis, such as that associated with tissue or organ rejection. In such instances, RF may serve as one of several serological markers for autoimmunity. The sensitivity of RF for established rheumatoid arthritis is only 60-70%, with a specificity of 78%.
But Caution is Needed When Testing Rheumatoid Factor
Many rheumatic conditions and other chronic inflammatory processes may produce rheumatoid factors. The presence of rheumatoid factor, especially in low titer, is far from diagnostic for rheumatoid arthritis. Furthermore, with increasing age, people with no clinical illness may have rheumatoid factor. IgM RFs have been reported in as much as 10% of the normal population. Statistically, patients with rheumatoid arthritis who have high titer rheumatoid factor are more likely to have severe disease and systemic involvement than other patients. Rheumatoid factor can be detected in synovial fluid, pleural fluid, and pericardial fluid but contributes little more than a positive serum test. Some rheumatoid factors may behave as cryoglobulins.
High Rheumatoid Factor Levels: What Do They Diagnose?
High levels of rheumatoid factor test (in general, above 20 IU/mL, 1:40, or over the 95th percentile; there is some variation among labs) occur in rheumatoid arthritis (present in 80%) and Sjögren's syndrome (present in 70%). The higher the level of RF, the greater the probability of destructive articular disease. It is also found in Epstein–Barr virus or Parvovirus infection and 5 to 10% of healthy persons, especially the elderly.
There is an association between rheumatoid factor and more persistently active synovitis, more joint damage, greater eventual disability, and arthritis.
Other than in rheumatoid arthritis, rheumatoid factor test may also be elevated in:
- Systemic lupus erythematosus (SLE)
- Juvenile Idiopathic Arthritis
- Sjögren syndrome
- Interstitial pulmonary fibrosis
- Hepatitis B, chronic liver disease, and chronic hepatitis
- Essential mixed cryoglobulinemia
- Primary biliary cirrhosis
- Infectious mononucleosis and any chronic viral infection
- Bacterial endocarditis
- Visceral leishmaniasis
- Systemic sclerosis
- After vaccination/transfusion in normal individuals
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