Educational Content: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare provider for diagnosis and treatment.
Definition of Rheumatoid factor
Medically reviewed by Min Clinic Staff | Updated: January 2026
Rheumatoid factor: An antibody that is measurable in the blood and is used to diagnose rheumatoid arthritis. Rheumatoid factor is present in about 80 percent of adults, and a much lower proportion of children, who have rheumatoid arthritis. It is also present in patients with other connective-tissue diseases, such as systemic lupus erythematosus, and in some patients with infectious diseases, such as infectious hepatitis.