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What is the rheumatoid factor test?

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A rheumatoid factor test measures the levels of rheumatoid factors (RF) that are present in a blood sample. Rheumatoid factors are antibodies produced by the immune system. The test can help in the diagnosis of rheumatoid arthritis (RA) and Sjogren's syndrome, states the National Institutes of Health's MedlinePlus.

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Rheumatoid factors can harm healthy tissues, and elevated levels of rheumatoid factors in a blood sample can be indicative of autoimmune diseases, such as rheumatoid arthritis, Sjogren's syndrome and lupus. For example, approximately 80 percent of adult patients with rheumatoid arthritis have high levels of these antibodies in their blood, notes MedicineNet. However, patients with hepatitis, mononucleosis and cancer can also have elevated levels of rheumatoid factors. Similarly, some healthy individuals may also have elevations in RF levels.

The normal levels for a RF blood test is lower than 40 to 60 units per milliliter, reports the National Institutes of Health's MedlinePlus. RF levels that are higher than this range can be indicative of rheumatoid arthritis or Sjogren's syndrome. To aid in a diagnosis of rheumatoid arthritis, doctors can order another blood test called anti-CCP antibody test. Although the RF test is useful in the diagnosis of rheumatoid arthritis or Sjogren's syndrome, it should not be used as a diagnostic test for other conditions, including hepatitis, leukemia, AIDS and mononucleosis.

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