Disease Activity Score 28 (DAS28) using C-reactive protein underestimates disease activity and overestimates EULAR response criteria compared with DAS28 using erythrocyte sedimentation rate in a large observational cohort of rheumatoid arthritis patients in Japan

OBJECTIVES: To compare disease activity and the improvement of disease activity evaluated between by Disease Activity Score 28 using erythrocyte sedimentation rate (DAS28-ESR) and by DAS28 using C-reactive protein (DAS28-CRP) in Japanese patients with rheumatoid arthritis (RA). METHODS: Data from 3073 RA patients registered in the large cohort database (NinJa: National Database of Rheumatic Diseases by iR-net in Japan) of 2003 was used to calculate DAS28-ESR and DAS28-CRP and disease activities were evaluated. Improvements in disease activities were also evaluated according to the European League Against Rheumatism (EULAR) response criteria in 1482 RA patients whose DAS28-ESR and DAS28-CRP could be calculated from data for both 2002 and 2003. RESULTS: The mean value of DAS28-CRP (3.59, SD 1.25) was significantly smaller than that of mean DAS28-ESR (4.31, SD 1.32) (p < 0.0001). The number of patients who satisfied the criteria of remission was 297 (9.7%) in DAS28-ESR versus 705 (22.9%) in DAS28-CRP and the number of patients with high disease activity was 842 (27.4%) versus 357 (11.6%) for DAS28-ESR and DAS28-CRP, respectively; there was a significant difference between the two (p < 0.0001). Change of respective DAS28 was significantly correlated (DeltaDAS28-ESR -0.05, SD 1.14 versus DeltaDAS28-CRP -0.10, SD 1.10) (p < 0.0001); however, the number of "good response" patients was significantly different (p < 0.03) between DAS28-ESR (97 patients, 6.5%) and DAS28-CRP (136 patients, 9.2%). CONCLUSIONS: DAS28-CRP significantly underestimated disease activity and overestimated the improvement in disease activity compared with DAS28-ESR. DAS28-CRP should be evaluated using different criteria from that for DAS28-ESR.