Rheumatoid Factor (IgM) – Serum/Plasma

Why Is This Test Done?

Your healthcare provider may order this test to help diagnose or monitor rheumatoid arthritis, lupus, or other autoimmune diseases. It can also be used to check for conditions like Sjogren’s syndrome or certain infections.

A positive rheumatoid factor result suggests an increased likelihood of autoimmune disease, but it doesn’t confirm a diagnosis alone. Other tests and clinical findings are needed for a full evaluation.

A positive result may appear in up to 25% of people without arthritis, so it’s important to discuss results with your doctor to understand the next steps.

A negative rheumatoid factor result means the test did not detect this specific antibody, but it doesn’t rule out other autoimmune conditions. Your doctor may recommend additional testing or follow-up.

A negative result could be common in people without autoimmune disease, so it doesn’t provide definitive proof of health in this context.

A blood sample is drawn from a vein, usually in your arm. The blood is then sent to a lab for analysis using an immunoassay method to detect rheumatoid factor antibodies.

No special preparation is needed, but you may be asked to avoid certain medications or foods for a short time if instructed by your provider.