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Rheumatoid Factor

RF IgM-RF
Serum (SST) IU/mL

About this test

Autoantibody (usually IgM) against the Fc fragment of IgG. Positive in ~70% of RA but also in many other conditions. Not highly specific.

Reference Ranges

Sex Age Range Notes
All ≥ 18 yrs < 20 Positive ≥20 IU/mL (lab-specific)

Clinical Interpretation

Low / Decreased
Seronegative RA is common (~30%).
High / Increased
Rheumatoid arthritis, Sjögren's syndrome, SLE, cryoglobulinaemia, infective endocarditis, hepatitis B/C, sarcoidosis.
Specimen
Serum (SST)
Reporting Unit
IU/mL
Category
🛡️ Immunology

⚠ Clinical Note
Reference ranges are indicative. Always interpret results in the context of the individual patient and local laboratory reference intervals, which may vary.