Rheumatoid factor (RF) is an immune system protein that can mistakenly attack healthy cells in the body. An RF test, a blood test used in diagnosing rheumatoid arthritis, measures the level of this protein. Understanding the normal range for rheumatoid factor is crucial in interpreting test results.
Rheumatoid factors are antibodies produced by the immune system. Normally, antibodies target germs to prevent illness, but rheumatoid factors can sometimes attack healthy cells and tissues. This characteristic is often linked with autoimmune diseases like rheumatoid arthritis and Sjogren syndrome. However, it’s important to note that rheumatoid factor may be present in healthy individuals and those with autoimmune diseases other than rheumatoid arthritis.
A positive rheumatoid factor test indicates high levels of rheumatoid factor in the blood. This test gained significance after rheumatoid factor was first associated with rheumatoid arthritis in 1940. For many years, a positive rheumatoid arthritis test was pivotal in diagnosing individuals exhibiting symptoms of the disease.
Approximately 80% of adults with rheumatoid arthritis have detectable rheumatoid factor in their blood. The rheumatoid factor test helps healthcare professionals in diagnosing rheumatoid arthritis. However, its presence is also sometimes noted in individuals without autoimmune conditions.
The rheumatoid factor test is notably specific for rheumatoid arthritis, with a 97% specificity rate. The development of a positive anti-CCP (anti-cyclic citrullinated peptide) is usually permanent, even during remission. About 20% of rheumatoid arthritis patients are seronegative, meaning their RF and anti-CCP lab results are negative. In these cases, the diagnosis relies on physical examination and other factors.
In terms of prevalence, 69% of people with rheumatoid arthritis will test positive for rheumatoid factor. The test’s sensitivity is 85%, implying that 15% of the general population might test positive without having rheumatoid arthritis.
For more detailed information on rheumatoid factor and its implications, visit Mayo Clinic, RheumatoidArthritis.org, Medical News Today, MedicineNet, MedlinePlus, Hospital for Special Surgery, and CreakyJoints.
