What tests are used to monitor rheumatoid arthritis (RA)?

Monitoring Rheumatoid Arthritis Disease Activity

The American College of Rheumatology recommends using one of six validated composite disease activity measures for monitoring RA: CDAI, DAS28 (ESR or CRP), PAS, PAS-II, RAPID-3, or SDAI, with selection based on your practice setting's resources and feasibility. 1

Recommended Disease Activity Measures

The ACR systematically evaluated 63 available RA monitoring tools and narrowed them to 6 validated measures that produce continuous indices with defined thresholds for remission, low, moderate, and high disease activity 1:

Patient-Reported Measures (No provider assessment or labs required)

• RAPID-3: Patient pain (VAS), patient global assessment, and Multidimensional HAQ (10 items, <3 minutes to complete) 1
• PAS-II: Patient pain (VAS), patient global assessment, and HAQ-II (10 items) 1
• PAS: Patient pain (VAS), patient global assessment, and original HAQ (41 items) 1

Advantage: Patients complete these in the waiting room on paper or electronic forms, making them highly practical when provider time or resources are limited 1

Caveat: These lack formal joint examination, which some consider important for face validity, though patient-reported measures may actually predict long-term outcomes better than provider joint counts 1

Provider-Assessed Measures (Require joint counts)

• CDAI: Simple addition of 28 tender joint count + 28 swollen joint count + patient global assessment + provider global assessment (no lab required, immediately calculable) 1, 2
• SDAI: Same as CDAI plus CRP (requires lab result) 1, 2
• DAS28: Complex formula incorporating 28 tender/swollen joint counts, patient global assessment, and ESR or CRP 1

Advantage: CDAI uses simple arithmetic without needing a calculator or lab results 1, 2

Caveat: Provider joint counts are examiner-dependent and may be unreliable if the assessor changes 1

Disease Activity Thresholds

CDAI (scale 0-76) 2:

• Remission: ≤2.8
• Low disease activity: >2.8 to 10.0
• Moderate disease activity: >10.0 to 22.0
• High disease activity: >22.0

SDAI (scale 0-86) 2:

• Remission: ≤3.3
• Low disease activity: >3.3 to ≤11.0
• Moderate disease activity: >11.0 to ≤26
• High disease activity: >26

Note: SDAI and CDAI provide more stringent remission definitions than DAS28 2

Monitoring Frequency

• Active disease: Measure disease activity every 1-3 months until remission is achieved 3
• Remission/low disease activity: Continue monitoring every 3-6 months to detect early relapse 3
• Any increase in inflammatory markers (ESR/CRP): Prompts clinical reassessment for disease reactivation 3

Laboratory Monitoring

Inflammatory Markers

• ESR and CRP: Incorporated into DAS28-ESR, DAS28-CRP, and SDAI scores, though these measures are not interchangeable 3
• Baseline labs: ESR, complete blood count, transaminases, renal function, urinalysis 3

Critical limitation: Anemia, azotemia, elevated immunoglobulins, and rheumatoid factor can artificially elevate ESR independent of inflammatory activity 3

Autoantibodies

• RF and anti-CCP: Useful for diagnosis but not for routine disease activity monitoring 4

Practical Implementation Algorithm

1. Choose your measure based on practice resources 1:

   • Limited time/no joint count training → Use RAPID-3 (patient-reported only)
   • Can perform joint counts but no immediate lab access → Use CDAI
   • Full resources with lab access → Use SDAI or DAS28

2. Establish baseline score at diagnosis 3

3. Monitor systematically 3:

   • Every 1-3 months during active disease
   • Every 3-6 months once remission/low disease activity achieved

4. Treat to target 1: Adjust therapy to achieve remission or low disease activity using your chosen measure's defined thresholds

Common pitfall: Switching between different measures during follow-up makes it difficult to track disease trajectory—select one measure and use it consistently 1