Disease activity level, remission and response in established rheumatoid arthritis: performance of various criteria sets in an observational cohort, treated with anti-TNF agents

Abstract

Background: Most composite indices of disease activity and response criteria in RA have been validated and compared in clinical trials rather than routine care. We therefore wanted to compare the performance of the DAS28, SDAI and CDAI activity indices, their activity states, their response criteria, and also compare with the ACR response criteria in an observational clinical setting.

Methods: Agreement between the criteria sets was investigated using kappa statistics in a non-randomized cohort of 1789 RA patients from southern Sweden, starting their first course of anti-TNF-treatment. Mean disease duration was 12 years. Completer analysis was used.

Results: Agreement between high, moderate and low activity states was moderate or substantial, with kappa = 0.5 or better for all criteria. Agreement between SDAI and CDAI disease states was > 90% in these categories with kappa > 0.8. DAS28 original and modified cut point remission had good agreement (kappa = 0.91). Agreement between responses was substantial at the overall/ACR20 level (about 95%, kappa = 0.7 or better) for all criteria. By contrast, agreement was poor between moderate and high level responses.

Conclusion: Disease activity states according to the various indices perform similarly and show substantial agreement at all levels except remission. Agreement between SDAI and CDAI states is excellent. Response criteria, applied at the individual patient level, are hard to interpret and show poor agreement, except at the lowest level of response. Thus, they should not be applied uncritically in clinical practice.

Figure 1

Disease stages at A) baseline and B) at 3 month follow up according to the different criteria sets. Notice that patients in remission are included in the low disease activity category, which thus comprises white and dotted areas together.

Figure 2

Response at 3 months according to different criteria sets. Notice that all ACR70 responders are include in the ACR50 responders, and all ACR50 responders are included in the ACR20 responders. Similarly EULARoverall responders include both good and intermediate responders, while SDAIoverall and CDAIoverall responders includes both major and minor responders