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The Rheumatoid Arthritis (RA) Factor test — commonly called Rheumatoid Factor (RF) — detects autoantibodies directed against th...
Also known as: RF Test · Rheumatoid Factor Test · RA Factor Blood Test · Quantitative RF · Rheumatoid Factor Quantitative
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The Rheumatoid Arthritis (RA) Factor test — commonly called Rheumatoid Factor (RF) — detects autoantibodies directed against the Fc portion of IgG immunoglobulins. These antibodies are found in the majority of patients with rheumatoid arthritis and are a standard component of the RA diagnostic workup. The quantitative RA Factor test provides a precise numerical titre — allowing correlation with disease severity and monitoring over time. When ordered alongside Anti-CCP (Test 63), it provides the most comprehensive serological assessment for RA diagnosis. No fasting required.
Key benefits of this package include:
What Does the Rheumatoid Arthritis (RA) Factor Test — Quantitative Measure?
| Level / Result | Possible Interpretation |
|---|---|
| < 14 IU/mL (Negative) | No significant RF detected — RA less likely, but seronegative RA (RF-negative) occurs in 20–30% of patients |
| 14–50 IU/mL (Weakly positive) | Low-titre RF — non-specific; many conditions and 5% of healthy elderly individuals are weakly RF-positive |
| 50–100 IU/mL (Positive) | Moderate RF — significantly suggestive of RA or other autoimmune condition; rheumatology evaluation recommended |
| > 100 IU/mL (Strongly positive) | High-titre RF — most specific for RA; predicts more severe, erosive disease; early specialist intervention important |
| RF positive + Anti-CCP positive (Double seropositivity) | Highest diagnostic specificity for RA — aggressive disease prognosis; early DMARD therapy strongly indicated |
Important Note: RF is sensitive (~70–80% of RA patients) but not specific (~70%) for RA — it can be positive in Sjogren's syndrome, SLE, viral hepatitis, TB, subacute bacterial endocarditis, and healthy elderly individuals. RF positivity alone does not diagnose RA — clinical criteria (joint involvement, symmetry, duration, elevated inflammatory markers) must be met. RF-negative (seronegative) RA occurs in 20–30% of RA patients — Anti-CCP detects many seronegative cases. All results must be reviewed by a rheumatologist or physician.
RF in Non-RA Conditions — Important Differential Diagnoses: RF positivity is not synonymous with RA. Conditions commonly associated with RF include: Sjogren's syndrome (RF positive in up to 90%), SLE (30–40%), mixed connective tissue disease (50–60%), subacute bacterial endocarditis (long-standing bacteraemia triggers RF production), chronic hepatitis C (40%), cryoglobulinaemia, and sarcoidosis. Healthy elderly individuals are RF-positive in 5–10% of cases with no disease. A positive RF therefore always requires clinical contextualisation rather than automatic RA labelling.
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