What is this test?
This test measures the IgM isotype of rheumatoid factor, an antibody that may occur in rheumatoid arthritis and other immune conditions.
Why might it be ordered?
- For persistent joint pain, morning stiffness or swelling when requested by a rheumatologist.
- To supplement assessment when total RF, Anti-CCP and clinical data are insufficient.
What sample is needed?
A healthcare professional collects a venous blood sample. Depending on the method, the laboratory uses serum or plasma.
How should you prepare?
Tell the laboratory about all medicines, hormone treatments, vitamins and supplements you take. Do not stop or change treatment unless your clinician tells you to. Follow any instructions about fasting and the time of collection.
How should you understand the result?
RF IgM may support the clinical assessment, but it does not by itself establish the presence or severity of rheumatoid arthritis. A positive result means the tested antibodies were detected, but it does not establish a diagnosis on its own. A negative result does not rule out every autoimmune condition.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.