What score is used to monitor rheumatoid arthritis?

Disease Activity Monitoring Scores for Rheumatoid Arthritis

The American College of Rheumatology recommends using validated composite disease activity measures including SDAI, CDAI, or DAS28 to monitor rheumatoid arthritis, with selection based on your practice resources and the need for laboratory results. 1, 2, 3

Primary Recommended Scores

Simplified Disease Activity Index (SDAI)

• Calculated as the numerical sum of five components: 28-joint tender count + 28-joint swollen count + patient global assessment (0-10 cm) + provider global assessment (0-10 cm) + C-reactive protein (mg/dL) 2, 4
• Disease activity categories: Remission ≤3.3, Low >3.3 to ≤11.0, Moderate >11.0 to ≤26, High >26 2, 3
• Advantages: Simple arithmetic addition without complex calculations, most sensitive and specific for predicting clinical decisions to change DMARDs, and SDAI ≤3.3 is an ACR/EULAR-recommended remission definition for clinical trials 1, 2
• Disadvantage: Requires waiting for CRP laboratory results, which may delay point-of-care decision making 1

Clinical Disease Activity Index (CDAI)

• Calculated as the sum of four components: 28-joint tender count + 28-joint swollen count + patient global assessment (0-10 cm) + provider global assessment (0-10 cm) 2, 3
• Disease activity categories: Remission ≤2.8, Low >2.8 to 10.0, Moderate >10.0 to 22.0, High >22.0 2, 3
• Key advantage: Does not require laboratory tests, making it immediately calculable at point of care for real-time clinical decisions 1, 2
• Provides more stringent remission criteria compared to DAS28 1, 2

Disease Activity Score-28 (DAS28)

• Uses a complex differential weighting formula incorporating 28 tender joint count (weighted more heavily than swollen joints), 28 swollen joint count, patient global assessment, and ESR (or CRP in DAS28-CRP variant) 1, 5
• Disease activity categories: Remission <2.6, Low ≤3.2, Moderate >3.2 to ≤5.1, High >5.1 6, 5
• Recommended by EULAR for assessing disease activity and treatment response 1, 5
• Important caveat: DAS28 remission criteria are less conservative than SDAI and CDAI, potentially underestimating disease activity in high ESR states with few active joints or meeting remission with significant swollen joints in low ESR states 1

Practical Selection Algorithm

Choose your monitoring score based on these practice considerations: 3

• Use CDAI when: You can perform reliable joint counts but lack immediate laboratory access, or when acute phase reactants are normal/near-normal 2, 6, 3
• Use SDAI when: You have full resources with laboratory access and CRP is elevated, as it provides objective inflammatory marker data 2, 6, 3
• Use DAS28 when: Your practice has established DAS28 infrastructure and you need EULAR-aligned monitoring, but recognize its less stringent remission thresholds 1, 5

Monitoring Frequency

• Measure disease activity every 1-3 months until remission is achieved 3
• Once remission or low disease activity is achieved, monitor every 3-6 months 3
• Treatment target should be sustained remission (SDAI ≤3.3 or CDAI ≤2.8) or low disease activity 1, 6, 3

Critical Implementation Requirements

Proper training in 28-joint count assessment is essential for accurate calculation of all three measures 2. The 28-joint assessment examines proximal interphalangeal joints, metacarpophalangeal joints, wrists, elbows, shoulders, and knees for both tenderness and swelling 6.

Common pitfall: ESR contributes 15% of information in DAS28-ESR, and newer biologic agents targeting specific inflammatory cytokines may disproportionately deflate composite scores that include acute phase reactants 1. This makes CDAI particularly valuable when biologics have normalized inflammatory markers but clinical synovitis persists 1, 6.

The SDAI and CDAI provide more stringent disease activity definitions compared to DAS28, making them superior for treatment decisions when aiming for true remission 1, 2, 7.