Laboratory Tests for Rheumatoid Arthritis
Test for rheumatoid factor (RF) in all patients with suspected RA who have synovitis, and add anti-cyclic citrullinated peptide (anti-CCP) antibodies if RF is negative or when considering combination therapy. 1, 2
Core Diagnostic Laboratory Tests
Autoantibody Testing
- Rheumatoid Factor (RF) should be ordered in every patient with suspected RA presenting with synovitis, as recommended by NICE guidelines 1
- Anti-CCP antibodies should be measured specifically when:
Inflammatory Markers
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) should be obtained to assess inflammation, though 40% of RA patients may have normal values 4, 5
- CRP correlates more closely with clinical and radiographic disease activity than ESR 6
Baseline Laboratory Assessment
- Complete blood count (CBC) with differential to identify anemia, thrombocytosis, or leukocytosis common in active RA 5, 7
- Comprehensive metabolic panel including liver function tests (ALT, AST) and renal function (creatinine) before initiating therapy 5, 7
- Hepatitis B and C screening plus tuberculosis testing before starting biologic DMARDs 5, 7
Critical Clinical Pitfall
Do not delay specialist referral based on negative laboratory results. Urgent rheumatology referral is indicated even when RF is negative and acute-phase reactants are normal, particularly when small joints of hands/feet are affected, multiple joints are involved, or symptoms have persisted ≥3 months 1, 2, 3. Remember that 30-40% of RA patients are RF-negative and 40% have normal inflammatory markers 2, 4.
Prognostic Value
Dual positivity for both RF and anti-CCP antibodies, especially at high titers, indicates higher risk for persistent, erosive disease and should prompt more aggressive early treatment 2, 6.