Conversion among the 28-joint count activity indices for rheumatoid arthritis

Area of Science:

• Rheumatology
• Clinical assessment
• Biostatistics

Background:

• Disease activity indices are crucial for rheumatoid arthritis (RA) management and research.
• Current RA indices (DAS28-ESR, DAS28-CRP, CDAI, SDAI) show correlation but lack agreement in patient classification.
• Discrepancies in disease activity categorization can impact clinical decisions and trial outcomes.

Purpose of the Study:

• To develop conversion formulas between four major 28-joint count RA disease activity indices.
• To establish new cutoff values for RA indices to minimize discrepancies in disease activity state categorization.
• To improve consistency in assessing rheumatoid arthritis disease activity.

Main Methods:

• Utilized data from 175 RA patients with concurrent CRP and ESR measurements.
• Established relationships between DAS28-ESR, DAS28-CRP, CDAI, and SDAI using regression analyses.
• Developed empiric conversion formulas and iteratively derived new cutoff values to reduce categorization disparities.

Main Results:

• Identified linear relationships between DAS28-ESR/DAS28-CRP and SDAI/CDAI; quadratic relationships for others.
• Natural logarithms and quadratic equations were used to model index relationships.
• Initial categorization disparities ranged from 9.7% to 40.6%, reduced to 6.3%-32.6% with new cutoff values.

Conclusions:

• Empiric formulas were successfully derived to interconvert DAS28-ESR, DAS28-CRP, CDAI, and SDAI values.
• New cutoff values significantly minimize discrepancies in rheumatoid arthritis disease activity state classification.
• These advancements offer improved standardization for RA assessment.