Rheumatoid factor - Mayo Clinic

OverviewA rheumatoid factor test measures the amount of rheumatoid factor in your blood. Rheumatoid factors are proteins made by your immune system that can attack healthy tissue in the body.High levels of rheumatoid factor in the blood are most often related to autoimmune diseases, such as rheumatoid arthritis and Sjogren syndrome. But rheumatoid factor may be detected in some healthy people. And sometimes people with autoimmune diseases have normal levels of rheumatoid factor.Products & ServicesA Book: Mayo Clinic Family Health BookA Book: Mayo Clinic Guide to ArthritisNewsletter: Mayo Clinic Health Letter — Digital Edition Why it's doneA rheumatoid factor test is one of a group of blood tests mainly used to help pinpoint a diagnosis of rheumatoid arthritis. These other tests may include:Anti-nuclear antibody (ANA).Anti-cyclic citrullinated peptide (anti-CCP) antibodies.C-reactive protein (CRP).Erythrocyte sedimentation rate (ESR, or sed rate).The amount of rheumatoid factor in your...