Rheumatoid Arthritis Disease Activity Assessment
Validated Measures
- The American College of Rheumatology recommends using validated measures like SDAI (Simplified Disease Activity Index) and CDAI (Clinical Disease Activity Index) for assessing rheumatoid arthritis disease activity 1
- SDAI is calculated as the sum of five components, including 28-joint swollen joint count, 28-joint tender joint count, provider global assessment of disease activity, patient global assessment of disease activity, and C-reactive protein measurement, with a scale of 0-86 1
- CDAI is calculated as the sum of four components, including 28-joint swollen joint count, 28-joint tender joint count, provider global assessment of disease activity, and patient global assessment of disease activity, with a scale of 0-76 1
- DAS28 (Disease Activity Score with 28-joint count) uses a more complex calculation requiring differential weighting of individual indices, and generally uses ESR, although DAS28-CRP is also available 2
Clinical Application and Advantages
- CDAI has the advantage of providing real-time results at the point of care without needing laboratory tests 2
- SDAI and CDAI use simple arithmetic addition, making them easier to calculate in clinical practice compared to DAS28 which requires a more complex formula 2, 1
- Treating to a target level (such as DAS28 ≤2.4) has been shown to improve rheumatoid arthritis outcomes 2
Important Considerations
- The inclusion of acute-phase reactants (like ESR or CRP) in measures like DAS28 and SDAI introduces additional variables and complexity 2
- ESR contributes approximately 15% of the information in the DAS28-ESR, which may lead to underestimation of remission in high ESR states with few active joints 2
- Newer biologic agents targeting specific inflammatory cytokines may disproportionately affect acute-phase reactants, potentially deflating composite scores 2