Rheumatoid Factor (RF)
Inflammation marker
Rheumatoid Factor
Rheumatoid Factor (RF)
An autoantibody (usually IgM) directed against the Fc portion of the body's own IgG. It is used mainly as a screening and classification aid for rheumatoid arthritis, but it is far from specific and can be raised in many other conditions.
PED Notes
Rheumatoid Factor has low specificity, so a positive result is not a diagnosis. It is elevated in rheumatoid arthritis but also in other autoimmune diseases (Sjogren's, lupus), chronic infections (hepatitis C, endocarditis), and simply with older age, and a meaningful minority of healthy people carry a low-titre positive with no disease. For an athlete with genuine inflammatory joint pain, morning stiffness, and swelling, RF is worth checking alongside anti-CCP (a more specific test), CRP, and ESR. In isolation, and especially at low titre, it is weak evidence and should not trigger alarm. Heavy training soreness and mechanical joint pain are not causes of a raised RF.
When high
When Rheumatoid Factor is positive/elevated:
- Interpret by titre and context. A low-titre positive in someone without joint symptoms is often a false alarm and needs no treatment, only clinical correlation.
- If there is genuine inflammatory arthritis (swollen, stiff joints, prolonged morning stiffness), pair RF with anti-CCP (anti-citrullinated peptide antibody, more specific for rheumatoid arthritis), CRP, and ESR, and refer to a rheumatologist. Early diagnosis and treatment materially change outcomes.
- Consider secondary causes of a raised RF: hepatitis C and other chronic infections, Sjogren's syndrome, lupus, and other autoimmune conditions.
- There is no supplement or protocol that "lowers" RF meaningfully; management is directed at the underlying diagnosis under specialist care.
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range
VitalMetrics Range