Normal value of rheumatoid factor

Rheumatoid factor (RF) is an autoantibody primarily detected in the blood of patients with rheumatoid arthritis (RA). The normal reference range for RF may vary slightly among different laboratories, but generally:

1. Enzyme-linked immunosorbent assay (ELISA): less than 20 IU/mL

2. Agar gel diffusion method: negative result

3. Immunoturbidimetric assay: less than 15 IU/mL

A positive RF result does not necessarily indicate RA, as positivity can also occur in other diseases or in a small number of healthy individuals. Additionally, a negative RF result does not completely rule out RA, especially in early-stage cases. When diagnosing RA, physicians make a comprehensive assessment based on clinical symptoms, physical signs, and other blood tests, such as anti-cyclic citrullinated peptide antibody (ACPA) testing.