A formula for calculating disease activity score with 28 joint counts (DAS28) with C-reactive protein (CRP) instead of the erythrocyte sedimentation rate (ESR) has been proposed.
Objective: Here we analyze the factors that contribute to the differences in the DAS28 when calculated using either the ESR (DAS28-ESR) or the CRP values (DAS28-CRP).
Methods: We analyzed the data from 587 visits made by 220 patients with early arthritis. The age at the onset of the disease was 51+/-16 years old and 76.3% of the patients were women. The disease evolution at the first visit was 5 months and at each visit information related to several variables was collected, including that necessary to calculate the DAS28-ESR and DAS28-CRP. We defined a new variable DIFDAS=DAS28-ESR-DAS28-CRP to analyze which independent variables account for differences between the two indexes.
Results: There was a correlation between the two indexes of 0.91 (p<0.0001), although the DAS28-ESR value obtained was higher than that of DAS28-CRP at approximately 90% of the visits. Significantly, the difference between both indexes was higher than 0.6 in 44% of the visits studied. A multivariate analysis showed that female gender and disease duration were associated with the higher values obtained for DAS28-ESR when compared to those of DAS28-CRP.
Conclusion: Our data show that DAS28-ESR and DAS28-CRP are not fully equivalent, because the former usually produces higher values. This finding is particularly relevant in females and patients with a long disease duration.