What blood tests are used to diagnose and manage rheumatoid arthritis?

Blood Tests for Rheumatoid Arthritis

Test for rheumatoid factor (RF) in all patients with suspected rheumatoid arthritis who present with synovitis, and add anti-cyclic citrullinated peptide (anti-CCP) antibodies if RF is negative or when considering combination therapy. 1, 2

Essential Diagnostic Blood Tests

Primary Serologic Testing

• Rheumatoid Factor (RF) should be offered to all patients with suspected RA who have synovitis, as recommended by NICE and the American College of Rheumatology 1, 2

  • RF is positive in 60-70% of RA patients, meaning 30-40% may be RF-negative 2
  • High RF titers correlate with progressive joint inflammation, erosions, and disability 3

• Anti-Cyclic Citrullinated Peptide Antibodies (anti-CCP) should be measured particularly in RF-negative patients and when combination therapy is being considered, per European League Against Rheumatism recommendations 1, 2

  • Anti-CCP has significant prognostic value; high levels and dual positivity with RF indicate higher risk of persistent and erosive disease 2
  • Anti-CCP is more specific for RA than RF alone 4, 5

Inflammatory Markers

• C-Reactive Protein (CRP) is preferred over ESR as it is simpler, more reliable, and not age-dependent for assessing disease activity 6

  • CRP correlates more closely than ESR with clinical and radiographic parameters of RA inflammation 3
  • Elevated CRP supports the diagnosis of RA in patients with inflammatory arthritis 4, 5

• Erythrocyte Sedimentation Rate (ESR) can be used but is less reliable than CRP 3

Baseline Laboratory Evaluation

Initial Workup Beyond Serologies

• Complete blood count with differential should be obtained at baseline 4
• Renal function tests are necessary before initiating disease-modifying antirheumatic drugs 4
• Hepatic function tests must be checked prior to starting DMARDs like methotrexate 4

Infectious Disease Screening

• Hepatitis B, Hepatitis C, and tuberculosis testing is required for patients being considered for biologic agents 4, 5

Critical Clinical Pitfall

Urgent specialist referral is mandatory even when blood tests are normal. Refer patients with suspected persistent synovitis urgently even if acute-phase response is normal or RF is negative, particularly when: 1, 2

• Small joints of hands or feet are affected
• More than one joint is involved
• There has been a delay of ≥3 months between symptom onset and seeking medical advice

This is crucial because seronegative RA exists and early treatment prevents irreversible joint damage and disability 1, 2

Monitoring Disease Activity

Ongoing Laboratory Assessment

• CRP should be measured regularly to guide treatment decisions and assess disease activity 6
• Composite disease activity measures (DAS28, SDAI, or CDAI) incorporating laboratory values should be used every 1-3 months until treatment target is reached 6, 7

The goal is achieving remission or near-remission, with laboratory markers serving as objective measures alongside clinical assessment 6, 8