Rheumatoid Factor (RF)

RF is an immunoglobulin present in the serum of 50 " “95% of adults with RA. It appears in serum and synovial fluid several months after onset of RA and is present up to years after therapy. The autoantibodies are usually of IgM class, although approximately 15% of RA has IgG class. Most methods detect only the IgM class.

Normal range: <20 IU/mL.

Use

Assisting in the diagnosis of RA, especially when clinical diagnosis is difficult

Interpretation

Increased In

Chronic hepatitis

Chronic viral infections

Cirrhosis

Dermatomyositis

Infectious mononucleosis

Leishmaniasis

Leprosy

Malaria

RA

Sarcoidosis

Scleroderma

Sj ƒ ¶gren syndrome

SLE

Syphilis

TB

Waldenstr ƒ ¶m macroglobulinemia

Limitations

RF is not a finding isolated to RA and may be present in a number of connective tissue and inflammatory diseases, including infectious mononucleosis, SLE, scleroderma, and hepatitis.

Older patients may have higher values.

Recent blood transfusion, multiple vaccinations or transfusions, or an inadequately activated complement may affect results.

Serum with cryoglobulin or high lipid levels may cause false-positive test results.