How do you assess disease activity in a patient with rheumatoid arthritis (RA)?

Assessment of Disease Activity in Rheumatoid Arthritis

The American College of Rheumatology recommends using standardized composite disease activity measures—specifically CDAI, SDAI, or DAS28—to assess disease activity at least yearly, with selection based on practice resources and the need for laboratory results. 1

ACR-Recommended Disease Activity Measures

The ACR identified six validated measures through systematic review of 63 tools, narrowing to those with the best psychometric properties and feasibility for clinical practice 1:

Patient-Driven Composite Tools (No Provider Assessment Required)

• PAS, PAS-II, and RAPID-3 can be completed by patients in the waiting room in less than 3 minutes, making them highly practical 1
• All three include: visual analog scale pain score, patient global assessment (PtGA), and a functional assessment tool (HAQ, HAQ-II, or MDHAQ respectively) 1
• Key advantage: No formal joint counts required, producing less random and more reliable measurements of change over time compared to examiner-dependent joint assessments 1
• Important limitation: Lack formal joint assessment and have not been directly studied for predicting long-term joint damage 1

Provider and Patient Composite Tools

• CDAI (Clinical Disease Activity Index) adds provider assessment (physician global assessment, 28 swollen joint count, 28 tender joint count) to patient global assessment 1

  • Scale 0-76: Remission ≤2.8, Low disease activity >2.8 to 10.0, Moderate >10.0 to 22.0, High >22.0 2
  • Major advantage: Simple numerical addition without calculator, no laboratory test required, immediately calculable at point of care 1, 2
  • Provides more stringent remission criteria than DAS28 2

• SDAI (Simplified Disease Activity Index) includes all CDAI components plus C-reactive protein 1

  • Scale 0-86: Remission ≤3.3, Low disease activity >3.3 to ≤11.0, Moderate >11.0 to ≤26, High >26 2
  • Advantage over CDAI: Includes objective inflammatory marker, particularly valuable when CRP is elevated 2
  • Disadvantage: Requires waiting for laboratory results, delaying calculation 2

• DAS28 (Disease Activity Score-28) incorporates 28-joint counts, patient global assessment, and acute-phase reactant (ESR or CRP) 1

  • EULAR-recommended for assessing disease activity and treatment response 1, 2
  • Important caveat: Less conservative remission criteria than SDAI and CDAI, making it less stringent for treatment decisions when aiming for true remission 2

Essential Components of Disease Activity Assessment

Clinical Examination

• 28-joint count assessment examining proximal interphalangeal joints (PIPs), metacarpophalangeal joints (MCPs), wrists, elbows, shoulders, and knees for tenderness and swelling 3
• Proper training in joint count assessment is essential for accurate calculation of composite measures 2

Patient-Reported Outcomes

• Pain assessment using visual analog scale 3
• Patient Global Assessment of Disease Activity (0-10 cm scale) 3
• Health Assessment Questionnaire Disability Index for functional status 3

Laboratory Markers

• C-reactive protein (CRP) is preferred over ESR as it is more reliable, not age-dependent, and provides validated, reproducible results 3
• Acute phase reactants should be measured at baseline and repeated when clinically relevant to monitor disease activity 3

Treatment Targets and Monitoring Frequency

The primary treatment target is sustained remission (SDAI ≤3.3 or CDAI ≤2.8) or low disease activity 3, 2:

• Monitor every 1-3 months until remission is achieved 2
• Monitor every 3-6 months once remission or low disease activity is achieved 2
• Disease activity should be classified as low, moderate, or high at least yearly using a standardized scale 1

Critical Clinical Pearls and Pitfalls

Selecting the Right Measure

• Choose CDAI when: Laboratory results are unavailable or normal, immediate point-of-care calculation is needed 2
• Choose SDAI when: CRP is elevated and objective inflammatory marker data is desired 2
• Choose patient-driven tools when: Provider time is limited or formal joint counts are not feasible 1

Common Pitfalls to Avoid

• Do not rely solely on acute phase reactants: ESR and CRP can be normal even in active disease and are poor predictors of RA 3
• Recognize examiner variability: Provider joint counts are highly examiner-dependent and may be unreliable if the assessor changes 1
• Beware of biologic effects: Biologic agents targeting inflammatory cytokines may disproportionately deflate scores that include acute phase reactants, making CDAI particularly valuable when biologics have normalized inflammatory markers but clinical synovitis persists 2
• SDAI and CDAI provide more stringent disease activity definitions compared to DAS28, making them superior for treatment decisions when aiming for true remission 2

Clinical Trial vs. Clinical Practice Reporting

• Clinical trials should report both disease activity states and response measures 1
• Response measures include ACR criteria (ACR20, ACR50, ACR70) and EULAR response criteria (good, moderate, non-responders) 1
• Report baseline disease activity levels, as these have relevance when interpreting results 1
• Report percentage of patients achieving low disease activity state and remission 1