What tests should be ordered for a rheumatology workup?

Standard Rheumatology Workup Tests

A comprehensive rheumatology workup should include acute phase reactants, autoantibody testing, and appropriate imaging studies to accurately diagnose and monitor rheumatic diseases. 1, 2

Core Laboratory Tests

• Complete Blood Count (CBC) with differential - Essential for detecting cytopenia, anemia, and neutropenia which can be present in various rheumatic diseases 2, 3

• Acute Phase Reactants:

  • C-reactive protein (CRP) - Preferred over ESR as it's more reliable, not age-dependent, and correlates more closely with clinical and radiographic parameters of inflammation 1, 4
  • Erythrocyte sedimentation rate (ESR) - Useful for assessing inflammation in rheumatoid arthritis, polymyalgia rheumatica, and temporal arteritis 2, 4

• Autoantibody Testing:

  • Rheumatoid Factor (RF) - Important for RA diagnosis, though 30-40% of RA patients may be seronegative 5, 4
  • Anti-citrullinated protein antibodies (ACPA) - High specificity for RA diagnosis and prognosis; negative tests don't exclude progression to RA 2, 5
  • Antinuclear antibodies (ANA) - Screening test for systemic lupus erythematosus and other connective tissue diseases 2, 6

• Additional Autoantibody Tests (when clinically indicated):

  • Antibodies to extractable nuclear antigens - Helpful for specific connective tissue disease diagnosis 2, 3
  • Anti-double-stranded DNA antibodies - Specific for SLE 2, 4
  • Anti-neutrophil cytoplasmic antibodies (ANCA) - Essential for diagnosing Wegener's granulomatosis 4, 3

• Other Laboratory Tests:

  • Biochemistry panel - Liver function tests, glucose, urate, and renal function 2, 6
  • Complement levels (C3, C4) - Useful for monitoring SLE activity 2, 3
  • Immunoglobulins - May be elevated in certain inflammatory conditions 2

Imaging Studies

• X-rays of affected joints - Should be performed at baseline, particularly hands, wrists, and feet to detect erosions which predict RA development and disease persistence 2

• Musculoskeletal ultrasound - Valuable for detecting early inflammatory changes in joints, tendons, and bursae; particularly useful for shoulder, elbow, wrist, and hand examinations 7

Disease-Specific Testing

• For suspected autoinflammatory diseases:

  • Genetic testing using next-generation sequencing (NGS) platforms for CAPS, TRAPS, MKD, and DIRA 8
  • Mevalonic acid in urine for suspected MKD 8

• For suspected Felty's syndrome:

  • Abdominal ultrasound or CT scan to confirm splenomegaly 6

Important Considerations

• Laboratory tests should support clinical findings from history and physical examination, not replace them 5, 9

• More than 30-40% of RA patients may have negative RF or ACPA tests or normal ESR/CRP, highlighting the limitations of laboratory testing 5

• When ordering autoantibody tests, consider the pretest probability of rheumatic disease to avoid misinterpretation of false positives 9, 10

• Repeat laboratory tests when clinically relevant to monitor disease activity and treatment response 2

• For undifferentiated peripheral inflammatory arthritis, X-rays of hands, wrists, and feet should be repeated within 1 year to assess for development of erosions 2

Common Pitfalls to Avoid

• Over-reliance on laboratory tests - No single test is diagnostic of any rheumatic disease; clinical correlation is essential 5, 9

• Failure to repeat testing - Single measurements may not reflect disease activity; serial testing is often necessary 2

• Inappropriate test ordering - Order tests based on specific clinical suspicion rather than as a general panel 9, 10

• Misinterpreting normal results - Normal laboratory values don't exclude rheumatic disease 5