Rheumatoid factor (RF) – quantitative test

A convenient test to assess the diagnosis, prognosis and course of joint disease. Rheumatoid arthritis is a chronic, progressive inflammatory disease of the connective tissues, mainly affecting the small joints of the fingers, wrists and hands. As inflammation progresses, antibody-antigen complexes are formed and deposited in the synovial tissue of the joint, leading to subsequent joint destruction. One of the main indicators used to diagnose this disease is the rheumatoid factor (RF). Rheumatoid factor is an immunoglobulin that is found in the blood of more than 80% of patients with rheumatoid arthritis. However, it can also be elevated in other conditions such as autoimmune disorders, connective tissue diseases and chronic infections. Low RF titres can be detected in 4% of normal healthy individuals and up to 20% in healthy elderly individuals.

The rheumatoid factor laboratory test is useful for the differential diagnosis of arthritis and for assessing the prognosis of arthritis. Juvenile rheumatoid arthritis usually does not cause an increase in rheumatoid factor. Rheumatoid factor levels are elevated in many diseases. A small increase may be unrelated to rheumatoid arthritis. The concentration of rheumatoid factor increases slightly with age. Higher levels of rheumatoid factor in the blood are proportionally more likely to lead to rheumatoid disease. The magnitude of the concentration correlates with the activity of the rheumatoid process. On the other hand, the absence of an increase in rheumatoid factor does not rule out the diagnosis of rheumatoid arthritis, as seronegative rheumatoid arthritis cases are common. The laboratory RF test can only rule out the diagnosis of rheumatoid arthritis in unclear cases. The biochemical automated test is incomparably more accurate than plate-based titration methods.

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