Background/Purpose: Assessment of disease activity is a key part of clinical decision in rheumatology care. High disease activity presented by disease activity score 28 ((DAS28) > 5.1 is used as a cutoff for biologic use in many countries include Korea. This study is to find confounding factors affecting erythrocyte sedimentation ratio (ESR) and C-reactive protein (CRP) to patients with rheumatoid arthritis to find the best tool to access rheumatoid arthritis (RA) disease activity, and to compare DAS28-ESR and DAS28-CRP to see whether we can use these indices interchangeably.

Methods:  A cross-sectional study was conducted in 1117 patients with RA, using initial registration data from Korean Biologics Registry (KOBIO).

Results: ESR levels were increased with age (r = 0.120, p < 0.001) and serum rheumatoid factor (r = 0.111, p = 0.001) but did not correlate with BMI, disease duration, and anti-CCP antibody titer. There were no differences in ESR levels according to the gender, smoking status, presence of diabetes mellitus, obesity (BMI ≥ 30) or low body weight (BMI < 20). CRP levels did not correlate with age, BMI, disease duration, RF and anti-CCP antibody. They were higher in female compared to male (p < 0.001) and higher in never-smoker compared to ever-smoker (p = 0.003). However, those differences of CRP levels were not significant when stratified by smoking status and gender, respectively. There were no differences in CRP levels according to the presence of diabetes mellitus, obesity (BMI ≥ 30) or low body weight (BMI < 18.5). In comparison of composite indices, DAS28CRP showed excellent correlation with DAS28ESR (r = 0.943, p < 0.001). However, in defining high disease activity, DAS28CRP showed only a fair agreement with DAS28ESR (kappa 0.381). To make best agreement with DAS28ESR in defining high disease activity, DAS28CRP need to be lowered to 4.5 (kappa 0.679, sensitivity 85.8%, specificity 88.0%, AUC 0.936).

Conclusion: DAS28CRP is a useful marker for inter-patient-comparison of RA disease activity when comparing patients with different age or rheumatoid factor status. DAS28CRP correlates well with DAS28ESR but the cutoff for high disease activity needs to be lowered to 4.5 to be used interchangeably with DAS28ESR in defining high disease activity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-of-disease-activity-score-das-28-crp-to-das28-esr-in-patients-with-active-rheumatoid-arthritis/