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Sunday, August 15, 2010

Rheumatoid Factor

Rheumatoid factor (RF) is an autoantibody that is produced by the body in response to certain disease states. Rheumatoid factor is usually an IgM antibody; however other classes of immunoglobulins can be produced. The antibody targets the Fc region of human IgG that is altered in protein structure. The RF autoantibodies attach themselves to healthy tissues throughout the body causing damage. The body can produce rheumatoid factor in response to various illnesses however it is most commonly measured to help diagnose potential cases of Rheumatoid Arthritis and Sjogren’s syndrome.

Rheumatoid factor can be present in a variety of illnesses. Around 75% of patients with Rheumatoid arthritis or Sjogren’s syndrome will present with a positive RF test. The remaining percentage of people with these two diseases will present with a negative level of RF or have very low levels. High RF levels can be found in patients with other autoimmune diseases such as lupus, scleroderma, and vasculitis. Positive RF tests can also be associated with diseases such as tuberculosis, malaria, hepatitis, endocarditis, and leukemia. Because RF levels may or may not be present in a patient with a specific illness RF is not used to definitively diagnose any disease.

Rheumatoid factor is measured in conjunction with other tests to help make a diagnosis. If Rheumatoid arthritis or Sjogren’s syndrome is suspected, a clinician might order other autoantibody tests such as an ANA (antinuclear antibody), anti-SS-A, or anti-SS-B to help differentiate between all possibilities. Performing a CRP level or a Sedimentation rate can help to determine if there is inflammation present. A newer test called the Cyclic Citrullinated Peptide Antibody (CCP) test can be ordered to detected early onset Rheumatoid Arthritis. This test can be performed in the event that RF levels are negative and the clinician still suspects Rheumatoid arthritis. Clinicians will use results from a variety of tests along with clinical findings to diagnose a patient with Rheumatoid arthritis.

Rheumatoid factor testing can be performed either by agglutination assays or through nephelometry. Here at BSHS we perform RF testing on the Dimension Vista system. The Vista uses nephelometry to measure levels of rheumatoid factor in a sample. The reagent includes polystyrene particles that are coated with anti-human IgG and a phosphate buffer. When the reagent is added to a patient’s sample any rheumatoid factor present will bind to the anti-human IgG. The aggregates that are formed scatter light in direct proportion to the concentration of RF present.

Normal values for rheumatoid factor can vary depending on testing methods. Agglutination methods will report results out as a titer. Nephelometric methods will report out rheumatoid factor as a unit of concentration. For the method utilized by the Dimension Vista, the normal range is less than 15 IU/mL. Factors that can affect results include excessively lipemic and icteric samples. Age can play a factor as well. High RF levels can be found in up to 10% of people over the age of 65 years. These potential false positive results should be taken into account when determining a diagnosis.

Rheumatoid factor is an autoantibody produced by the body for unknown reasons. It attaches to various tissues in the body causing damage and subsequent illness. Clinicians will measure levels of rheumatoid factor in the body in order to determine if a patient potentially has rheumatoid arthritis or Sjogern’s syndrome. While there is no definitive test to diagnosis rheumatoid arthrisis, testing for RF in conjunction with others assays and clinical findings can help clinicians in diagnosing potential cases of rheumatoid arthritis.

• SIEMENS Dimension Vista Flex reagent cartridge. (2008). RF. (REF K7068). Newark, DE: Siemens Healthcare Diagnostics Inc.
• Rheumatoid Factor. (2010). Rheumatoid Factor: The Test. Lab Tests Online. Retrieved on July 18, 2010 from http://www.labtestsonline.org/understanding/analytes/rheumatoid/test.html
• Arthritis Health Center: Rheumatoid Factor. (2008). Rheumatoid Factor. WebMD. Retrieved on July 18, 2010 from http://www.arthritis.webmd.com/rheumatoid-factor-rf

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