Background Assessment of disease activity is a key part of clinical decision in rheumatology care. High disease activity presented by DAS28 >5.1 is used as a cutoff for biologic use in many countries include Korea, while remission (DAS28 <2.6) is considered as a goal of therapy.
Objectives We compared the DAS28ESR and DAS28CRP to other RA activity measures and were to find confounding factors affecting acute phase reactants to patients with rheumatoid arthritis to find best tool to access RA disease activity.
Methods A cross-sectional study was conducted in 1120 patients with RA, using initial registration data from Korean Biologics Registry (KOBIO).
Results In comparison of composite indices, DAS28CRP showed excellent correlation with SDAI (r =0.926, p<0.001), CDAI (r =0.901 p<0.001). DAS28ESR also showed good correlation with SDAI (r =0.875, p<0.001) and CDAI (r =0.886, p<0.001). In defining high disease activity, DAS28CRP showed an excellent agreement with DAS28ESR (kappa 1.000). However, in defining remission, DAS28CRP showed a fair agreement with DAS28ESR (kappa 0.317, 95%CI 0.137 to 0.497). Compared CDAI remission (≤2.8), DAS28ESR showed a fair agreement (kappa 0.331, 95%CI -0.014 to 0.675) and DAS28CRP showed a poor agreement (kappa 0.104, 95%CI -0.031 to 0.238).
In comparison of acute phase reactants to other disease activity measures, CRP showed low but significant correlation with SJC (r =0.132, p<0.001), TJC (r =0.087, p=0.004), SDAI (r =0.441, p<0.001), CDAI (r =0.134, p<0.001) and RAPID3 score (r =0.139, p<0.001). ESR also showed significant correlation with SJC (r =0.132, p<0.001), TJC (r =0.063, p=0.035), SDAI (r =0.233, p<0.001), CDAI (r =0.145, p<0.001) and RAPID3 score (r =0.166, p<0.001).
In correlation analysis using CDAI as controlled variable, ESR increased with age (r =0.110, p<0.001) and serum rheumatoid factor (r =0.105, p=0.001) but was not correlated with BMI, disease duration, and anti-CCP Ab titer. There was no difference in ESR according to the gender, smoking status, presence of diabetes mellitus, obesity (BMI ≥30) or low body weight (BMI <20).
In the same analysis, CRP was not correlated with age, BMI, disease duration, RF and anti-CCP antibody. It was higher in male compared to female (3.41 ± 3.60 vs 2.42 ± 4.08 mg/dL, p=0.001) and higher in ever-smoker compared to never-smoker (3.23 ± 3.46 vs. 2.48 ± 4.10 mg/dL, p=0.027). There was no difference in CRP according to the presence of diabetes mellitus, obesity (BMI ≥30) or low body weight (BMI <18.5).
Conclusions Both DAS28CRP and DAS28ESR were well correlated with other activity indices and showed an excellent agreement in defining high disease activity. ESR increased with age but was less susceptible to gender or smoking status compared to CRP, suggesting DAS28ESR to be a more useful marker for inter-patient-comparison of RA disease activity.
Disclosure of Interest None declared