Monitoring Disease Activity in Rheumatoid Arthritis
Use one of six validated composite disease activity measures (CDAI, DAS28-ESR, DAS28-CRP, SDAI, RAPID-3, PAS, or PAS-II) at every visit, measuring every 1-3 months during active disease and every 3-6 months once remission or low disease activity is achieved. 1
Recommended Disease Activity Measures
The American College of Rheumatology systematically evaluated 63 monitoring tools and identified six validated measures that accurately reflect disease activity, are sensitive to change, discriminate between disease activity states, and are feasible at point of care 2:
Provider-Assessed Measures (Require Joint Counts)
CDAI (Clinical Disease Activity Index): Sum of 28 tender joint count + 28 swollen joint count + patient global assessment (0-10 scale) + provider global assessment (0-10 scale), with no laboratory requirement, making it immediately calculable at point of care 1, 3
SDAI (Simplified Disease Activity Index): CDAI components plus CRP (mg/dL), requiring laboratory results but providing objective inflammatory marker data 1, 3
DAS28 (Disease Activity Score-28): Complex formula incorporating 28 tender/swollen joint counts, patient global assessment, and ESR or CRP 1, 5
Patient-Reported Measures (No Joint Counts Required)
RAPID-3: Patient pain + patient global assessment + Multidimensional HAQ, completed in less than 3 minutes 1
PAS: Patient pain + patient global assessment + original HAQ 1
PAS-II: Patient pain + patient global assessment + HAQ-II 1
Practical Selection Algorithm
Choose your measure based on available resources 1, 3:
Limited time/no joint count training: Use RAPID-3, PAS, or PAS-II (patient-reported measures) 1
Can perform joint counts but no immediate lab access: Use CDAI (no laboratory requirement, immediately calculable) 1, 3
Full resources with immediate lab access: Use SDAI or DAS28-CRP (includes objective inflammatory markers) 1, 3
Traditional practice with ESR: Use DAS28-ESR, though recognize it is not interchangeable with DAS28-CRP 2, 1
Monitoring Frequency
Establish a baseline score at diagnosis, then follow this schedule 1, 3:
Active disease: Measure every 1-3 months until remission is achieved 1, 3
Remission or low disease activity: Measure every 3-6 months to detect early relapse 1, 3
Critical Implementation Considerations
Proper training in 28-joint count assessment is essential for accurate calculation of CDAI, SDAI, and DAS28 3. The 28-joint count includes bilateral shoulders, elbows, wrists, MCPs (1-5), PIPs (1-5), and knees 6.
CDAI and SDAI provide more stringent remission criteria than DAS28 2, 3, 7. DAS28 tends to overestimate remission, with remission rates differing considerably between measures (kappa=0.418 for agreement on disease activity categories) 7. When aiming for true remission, CDAI or SDAI are superior choices 3.
Biologic agents targeting specific inflammatory cytokines may disproportionately deflate composite scores that include acute-phase reactants 2, 3. CDAI is particularly valuable when biologics have normalized inflammatory markers but clinical synovitis persists 3.
Comorbid conditions can confound measurements: Anemia, azotemia, and fibromyalgia elevate acute-phase reactants or result in tender joints independent of RA activity 2. In these cases, interpret individual components rather than relying solely on the total score 3.
Baseline Laboratory Assessment
Obtain at diagnosis 1:
- ESR
- Complete blood count
- Transaminases
- Renal function
- Urinalysis
Treatment Target
The ultimate goal is sustained remission (SDAI ≤3.3 or CDAI ≤2.8) or low disease activity 3. However, remission may not be appropriate for all patients due to comorbidities, treatment toxicity, or patient preference 2. Despite these complexities, standardized assessment facilitates treating to target, which improves disease outcomes 2.
Quality Reporting
Routine use of these validated measures allows clinicians to demonstrate high-quality care for RA, as measured by nationally endorsed quality measures 2. Incorporation into practice workflow facilitates adherence to ACR treatment guidelines and provides necessary tools for treating to target 2, 1.