The Rheumatoid Factor (RF) test is used to detect and measure autoantibodies associated with diseases such as rheumatoid arthritis (RA). RF generally refers to antibodies that react against the Fc portion of immunoglobulin G (IgG). The test is typically performed using methods such as nephelometry or ELISA, and it measures the level of RF in the blood.
Elevated levels of RF (usually above 14–20 IU/mL, depending on the laboratory kit) may suggest rheumatoid arthritis, but a positive result alone is not definitive, as RF can also be found in other autoimmune diseases (such as Sjögren’s syndrome and lupus), chronic infections (like hepatitis C), and even in healthy elderly individuals.
On the other hand, around 20–30% of RA patients may have negative RF (seronegative RA). Therefore, interpretation of the results must be done in conjunction with clinical symptoms, physical examination, and additional tests such as anti-CCP antibodies (anti-cyclic citrullinated peptide antibodies). This test is also useful for monitoring disease activity or treatment response in patients with rheumatoid arthritis.
