Rheumatoid Factor (RF) Measurement in Serum or Plasma

What Is Rheumatoid Factor?

Rheumatoid factor is an antibody that can attack your own healthy cells in some people. It’s often tested when doctors suspect rheumatoid arthritis or other autoimmune disorders, though it’s not definitive on its own. Levels can vary widely and may not always correlate with disease activity.

Why Might You Need This Test?

Your healthcare provider may order this test if you have symptoms like joint pain, swelling, or fatigue, or if you have a family history of autoimmune diseases. It can also be used as part of a broader evaluation for conditions like lupus, Sjogren’s syndrome, or other inflammatory diseases.

What Does a Positive Result Mean?

A positive rheumatoid factor result suggests an increased likelihood of an autoimmune condition, but it doesn’t confirm a diagnosis. Many people with rheumatoid arthritis test positive, but some without the disease also do. Results should be interpreted alongside other clinical findings and tests.

How Is This Test Performed?

Blood is drawn from a vein in your arm, and the sample is tested for rheumatoid factor using an immunoassay method. The test checks for antibodies that bind to the Fc portion of other antibodies, which is how rheumatoid factor works.