What labs should be checked to diagnose and manage arthritis?

Laboratory Tests for Diagnosing and Managing Arthritis

Essential blood work for diagnosing and monitoring arthritis should include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), and anti-citrullinated protein/peptide antibodies (anti-CCP), along with a complete blood count and basic biochemistry. 1

Core Laboratory Tests for Arthritis Evaluation

Inflammatory Markers

• ESR and CRP: Should be performed at baseline for diagnosis and prognosis of inflammatory arthritis and repeated when clinically relevant 2
  • ESR shows diagnostic value for rheumatoid arthritis (RA) development
  • CRP has some usefulness in predicting RA, especially at higher levels
  • Both tests have limitations - more than 40% of RA patients may have normal ESR or CRP 3

Autoantibody Testing

• Rheumatoid Factor (RF):

  • Sensitivity: 69-84%, Specificity: 78-85% 1
  • Higher sensitivity but lower specificity than anti-CCP

• Anti-CCP Antibodies:

  • Sensitivity: 67-78.5%, Specificity: 95-98% 1
  • Highest specificity for RA diagnosis
  • Included in 2010 ACR/EULAR classification criteria for RA

Additional Basic Laboratory Tests

• Complete Blood Count (CBC)

  • Helps identify anemia of chronic disease common in inflammatory arthritis
  • One of the most commonly ordered tests for RA monitoring 4

• Biochemistry Panel:

  • Liver function tests
  • Renal function tests
  • Glucose and urate levels 2
  • Important for baseline assessment and medication monitoring

Extended Testing Based on Clinical Suspicion

• Antinuclear Antibodies (ANA):

  • Less specific for RA, more relevant for other autoimmune conditions like SLE 1
  • Should be ordered when systemic autoimmune diseases are suspected

• Additional Immunologic Tests (when indicated):

  • Antibodies to extractable nuclear antigens
  • Antibodies to double-stranded DNA
  • Immunoglobulin levels 2

• HLA Typing:

  • HLA-B27 for suspected spondyloarthropathies
  • HLA-DR for specific RA subtypes 2

Interpretation and Clinical Correlation

• Laboratory tests should be interpreted in the context of clinical findings
• Discordance between ESR and CRP occurs in about 28% of cases 5
• When discordance occurs, CRP is generally a better measure of disease activity than ESR 5
• The combination of ESR and CRP yields more useful information than either test alone 5

Limitations and Caveats

• More than 30% of patients with RA have negative tests for RF or anti-CCP antibodies 3
• Laboratory tests cannot serve as a gold standard for diagnosis and management in all individual patients 3
• Patients perceive CRP as most helpful in understanding their disease activity 4
• Some research suggests fibrinogen may be superior to ESR in assessing RA disease activity 6, though this is not yet standard practice

Monitoring Approach

• ESR and CRP should be repeated when clinically relevant to assess disease activity and treatment response 2
• Regular monitoring of CBC and biochemistry is essential when patients are on disease-modifying antirheumatic drugs (DMARDs) to detect potential toxicity 1
• Patients worry about treatment effectiveness and value accurate laboratory monitoring 4

Laboratory testing is just one component of arthritis evaluation and should always be interpreted alongside a careful systematic history and physical examination with attention to joint patterns, symptom duration, and extra-articular features 2.