What labs are recommended to diagnose polyarthralgia (polyarticular pain) of the wrists, hands, shoulders, and one knee?

Laboratory Tests for Diagnosing Polyarthralgia of Wrists, Hands, Shoulders, and One Knee

For polyarthralgia affecting multiple joints including the wrists, hands, shoulders, and knee, initial laboratory evaluation should include ESR, CRP, RF, and ACPA testing, followed by additional tests based on the suspected differential diagnosis. 1

Initial Laboratory Evaluation

• Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) should be performed at baseline for both diagnosis and prognosis of undifferentiated peripheral inflammatory arthritis, with repeat testing when clinically indicated 1

• Rheumatoid Factor (RF) and Anti-Citrullinated Protein Antibodies (ACPA) testing is essential as these factors are predictive of rheumatoid arthritis diagnosis and prognosis, though negative tests do not exclude progression to RA 1

• Complete Blood Count (CBC) to assess for anemia of chronic disease, leukocytosis (infection), or other hematologic abnormalities 2, 3

• Basic metabolic panel to evaluate renal function and electrolyte abnormalities that may be associated with certain rheumatologic conditions 2

• Urinalysis to screen for renal involvement in systemic rheumatic diseases 2

Additional Testing Based on Clinical Suspicion

• Additional autoantibody tests should be considered if a connective tissue disease or systemic inflammatory disorder is suspected 1:

  • Antinuclear antibody (ANA) for systemic lupus erythematosus and other connective tissue diseases
  • Anti-dsDNA and anti-Sm for lupus
  • Anti-Ro/SSA and anti-La/SSB for Sjögren's syndrome

• HLA-B27 testing may be helpful in specific clinical settings, particularly when spondyloarthropathies are suspected 1

• Uric acid levels if crystal arthropathy (gout) is suspected 2

• Thyroid function tests to rule out thyroid disorders that can present with polyarthralgia 4

• Serum cortisol and ACTH levels if adrenal insufficiency is suspected, especially with accompanying symptoms like fatigue, hypoglycemia, or hyponatremia 4

Synovial Fluid Analysis

• Joint aspiration and synovial fluid analysis should be performed when there is joint effusion, particularly to rule out:
  • Crystal-induced arthritis (examination for urate or calcium pyrophosphate crystals)
  • Septic arthritis (cell count, Gram stain, culture)
  • Inflammatory arthritis (cell count, protein) 2, 3

Imaging to Complement Laboratory Testing

• X-rays of affected joints should be performed at baseline, with particular attention to hands, wrists, and feet as the presence of erosions is predictive for the development of RA and persistence of disease 1

• MRI of hands and wrists could be considered for diagnosis if there is suspicion of RA, as it can detect early inflammatory changes not visible on conventional radiographs 1, 5

Clinical Predictors to Guide Laboratory Testing

When ordering labs, consider these predictors of persistent inflammatory arthritis:

• Disease duration ≥6 weeks
• Morning stiffness >30 minutes
• Involvement of small joints and/or knee
• Involvement of ≥3 joints
• Functional impairment 1

Pitfalls to Avoid

• Overreliance on negative RF or ACPA results - these can be negative in early RA 1

• Failure to consider non-rheumatologic causes of polyarthralgia such as endocrine disorders, viral infections, or paraneoplastic syndromes 4, 2

• Neglecting to repeat laboratory tests when clinically indicated, as serological markers may evolve over time 1

• Focusing only on inflammatory markers without considering the full clinical picture, as some inflammatory conditions may present with normal ESR/CRP 2, 3