Rheumatoid factor (RF) is a protein produced by the immune system that can attack healthy cells in the body. An RF test measures the amount of rheumatoid factor in the blood and is used to help diagnose rheumatoid arthritis (RA). Normal levels of rheumatoid factor in the blood are typically less than 20 IU/mL (international units per milliliter), but this can vary slightly depending on the laboratory’s specific reference range.
Levels of RF higher than the normal range can be associated with autoimmune diseases, particularly rheumatoid arthritis. However, elevated rheumatoid factor levels can also occur in other conditions and are not exclusive to RA. A positive RF test indicates a high level of rheumatoid factor in the blood, which may necessitate further investigation for rheumatoid arthritis or other related conditions.
The rheumatoid factor test is part of a group of blood tests used to diagnose rheumatoid arthritis, which may also include tests for anti-nuclear antibody (ANA), anti-cyclic citrullinated peptide (anti-CCP) antibodies, C-reactive protein (CRP), and the erythrocyte sedimentation rate (ESR or sed rate). While a positive RF test can suggest rheumatoid arthritis, it is not definitive, and rheumatoid factor can be present in other diseases as well.
According to the Mayo Clinic, higher levels of rheumatoid factor in the blood are closely associated with autoimmune diseases, especially rheumatoid arthritis. Moreover, depending on the method used, rheumatoid factor is present in the serum of a majority of patients with rheumatoid arthritis, ranging from 60% to 85% positivity with varying rates of false positives.
For more detailed information on rheumatoid factor and associated tests, resources such as Medical News Today, HealthCentral, and Labcorp can provide additional insights.
