The Rheumatoid Factor (RA Factor) Test is a blood test used to measure the ...
level of rheumatoid factor (RF) antibodies in the blood. Rheumatoid factor is an autoantibody—a type of protein produced by the immune system that mistakenly attacks healthy tissues, primarily in the joints.
What the RA Factor Test Measures
Presence of Rheumatoid Factor (RF):
The test detects RF autoantibodies in the blood, which are commonly associated with rheumatoid arthritis (RA) and other autoimmune diseases.
RF Levels in Blood (Quantitative Test):
The test measures RF concentration, usually in IU/mL (International Units per Milliliter).
A normal RF level is typically less than 14 IU/mL, though reference ranges may vary between laboratories.
Diagnosis of Autoimmune Diseases:
While RA Factor is strongly linked to rheumatoid arthritis, it may also be elevated in other autoimmune disorders, such as:
Differentiation of Rheumatoid Arthritis from Other Conditions:
A positive RF test suggests a higher likelihood of RA but does not confirm the diagnosis on its own. Additional tests, such as Anti-CCP (Cyclic Citrullinated Peptide) antibodies, CRP (C-reactive protein), and ESR (Erythrocyte Sedimentation Rate), are used to confirm the condition.
Interpreting RA Factor Test Results
RF Level (IU/mL)
Interpretation
< 14 IU/mL
Normal (Negative) – Low risk of RA
14-50 IU/mL
Mildly elevated – Possible early RA or other autoimmune conditions
50-100 IU/mL
Moderately elevated – Higher chance of RA or chronic inflammatory disease
>100 IU/mL
Strongly positive – Indicates severe RA or advanced autoimmune disorder
Limitations of the RA Factor Test
False Positives – Some healthy individuals may test positive for RF without having RA.
False Negatives – Early-stage rheumatoid arthritis patients may have normal RF levels.
Additional Testing Required – Doctors may order Anti-CCP and CRP/ESR tests for a conclusive diagnosis.
The RA Factor Test is a helpful diagnostic tool but should always be interpreted alongside clinical symptoms and additional lab findings.
