Rheumatoid Factor Test: Understanding RA Diagnosis

What is Rheumatoid Factor?

Rheumatoid factor (RF) is an antibody produced by the immune system that attacks body's own tissues. The rheumatoid factor test measures this antibody in blood. While associated with rheumatoid arthritis, RF can appear in other autoimmune diseases and sometimes even in healthy individuals.

Understanding the RF Test

Test Results

RF is measured in IU/mL or RF units. Normal is less than 14 IU/mL. Positive RF (higher than normal range) suggests autoimmune disease, but a single positive result doesn't diagnose rheumatoid arthritis. Clinical symptoms and other tests must be considered.

Seropositive vs Seronegative

• ✓ Seropositive RA: RF-positive (60-70% of RA patients)
• ✓ Seronegative RA: RF-negative but may have anti-CCP antibodies (30-40% of RA patients)

Related Tests

1. Anti-CCP Antibodies

More specific for rheumatoid arthritis than RF. Early and more sensitive predictor of RA. Present in 95% of RA patients, even before symptoms appear.

2. Antinuclear Antibodies (ANA)

Tests for antibodies to cell nuclei. Can indicate lupus, Sjögren's syndrome, or other autoimmune diseases. Often done alongside RF testing.

3. Erythrocyte Sedimentation Rate (ESR)

Measures inflammation in blood. Elevated in rheumatoid arthritis and other inflammatory conditions. Used to monitor disease activity.

4. C-Reactive Protein (CRP)

Another inflammation marker. More specific than ESR. Elevated in active RA and decreases with successful treatment.

Conditions Associated with Positive RF

• ✓ Rheumatoid arthritis (60-70% of patients)
• ✓ Systemic lupus erythematosus (SLE)
• ✓ Sjögren's syndrome
• ✓ Scleroderma
• ✓ Vasculitis
• ✓ Chronic infections (hepatitis C, tuberculosis)
• ✓ Healthy individuals (5-15%)

Symptoms of Rheumatoid Arthritis

• • Joint pain, swelling, and stiffness (especially hands and feet)
• • Morning stiffness lasting more than 30 minutes
• • Fatigue and general malaise
• • Low-grade fever
• • Loss of appetite and weight loss
• • Symmetric joint involvement (both sides of body)

Diagnostic Criteria

RA diagnosis requires meeting clinical criteria including symptom duration (6 weeks or more), joint involvement, RF or anti-CCP positivity, and elevated inflammatory markers. Early diagnosis enables prompt treatment to prevent joint damage.