What blood tests are used for arthritis screening?

Recommended Blood Tests for Arthritis Screening

The essential blood tests for arthritis screening include complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), antinuclear antibodies (ANA), and liver function tests. 1, 2

Core Laboratory Tests for Arthritis Screening

Inflammatory Markers

• ESR and CRP
  • Should be performed at baseline for both diagnosis and prognosis 1
  • Indicate ongoing inflammation but are not specific to any particular type of arthritis 2
  • Should be repeated when clinically relevant 1

Autoantibodies

• Rheumatoid Factor (RF) and Anti-CCP (ACPA)

  • Must be tested in all patients with suspected inflammatory arthritis 1
  • Anti-CCP: 67-78.5% sensitivity, 95-98% specificity (highest specificity for RA) 2
  • RF: 69-84% sensitivity, 78-85% specificity (higher sensitivity but lower specificity than Anti-CCP) 2
  • Negative tests do not exclude progression to RA 1

• Antinuclear Antibodies (ANA)

  • Should be considered if systemic connective tissue disease is suspected 2
  • Less specific for RA, more relevant for other autoimmune conditions 2

Basic Laboratory Panel

• Complete Blood Count (CBC)

  • Essential baseline investigation before establishing diagnosis 1
  • Helps exclude other causes of joint symptoms 1

• Liver Function Tests

  • Transaminases should be checked to exclude other diseases 1
  • Important baseline before potential DMARD therapy 2

• Urinalysis

  • Recommended as part of the basic screening panel 1

Additional Tests Based on Clinical Suspicion

• HLA-B27

  • Not routinely recommended 1
  • May be helpful in specific clinical settings (e.g., suspected spondyloarthropathy) 1

• Additional Autoantibody Tests

  • Consider if connective tissue disease/systemic inflammatory disorder is suspected 1
  • May include antibodies to extractable nuclear antigens, anti-dsDNA 1

• Thyroid Function Tests

  • Can help rule out thyroid disorders that can present with joint pain 2

Imaging Studies to Complement Blood Tests

• X-rays of affected joints

  • Should be performed at baseline 1, 2
  • X-rays of hands, wrists, and feet should be considered as presence of erosions predicts development of RA 1

• Ultrasound and MRI

  • Not recommended for routine use 1
  • MRI of hands and wrists could be considered when RA is suspected 1, 2

Diagnostic Algorithm

1. Initial Screening: Order CBC, ESR, CRP, RF, anti-CCP, liver function tests, and urinalysis for all patients with suspected inflammatory arthritis
2. Based on Clinical Features:
   • If small joint involvement predominates: Focus on RF and anti-CCP
   • If systemic symptoms present: Add ANA testing
   • If axial symptoms predominate: Consider HLA-B27
3. Interpret Results in Clinical Context:
   • Positive RF and/or anti-CCP with elevated inflammatory markers strongly suggests RA
   • Negative autoantibodies with elevated inflammatory markers may indicate seronegative arthritis
   • Positive ANA may suggest connective tissue disease

Common Pitfalls to Avoid

• Overreliance on a single test can lead to misdiagnosis 2
• Negative RF and anti-CCP do not exclude RA diagnosis 2
• Elevated inflammatory markers can occur in various conditions including infections and malignancies 2
• Delayed referral to a rheumatologist (should be within 6 weeks of symptom onset) 1, 2

Remember that laboratory tests should be interpreted in the context of clinical findings, as no single test can definitively diagnose or exclude inflammatory arthritis.