Correlation of rheumatoid arthritis activity indexes (Disease Activity Score 28 measured with ESR and CRP, Simplified Disease Activity Index and Clinical Disease Activity Index) and agreement of disease activity states with various cut-off points in a Northeastern Brazilian population

Abstract

IntroductionThe Disease Activity Score 28 (DAS28) and its versions have been used to measure rheumatoid arthritis activity, but there is no consensus about which one is the best. ObjectivesDetermine the correlation among indexes (DAS28 ESR, DAS28 CRP, SDAI and CDAI) and evaluate agreement of activity strata using different cut-off points. MethodsRheumatoid arthritis patients were cross-sectionally evaluated with data collection to calculate the DAS28 (ESR and CRP), SDAI and CDAI, using different cut-offs for defining remission, mild, moderate and high activity. Pearson correlations were calculated for continuous measures and agreement (kappa test) for the strata (remission, mild, moderate and high activity). ResultsOf 111 patients included, 108 were women, age 55.6 years, 11-year disease duration. DAS28 (ESR) was significantly higher than DAS28 (CRP) (4.0 vs. 3.5; p<0.001) and the values remained higher after stratification by age, gender, disease duration, rheumatoid factor and HAQ. Correlations among indexes ranged from 0.84 to 0.99, with better correlation between SDAI and CDAI. Agreements among activity strata ranged from 46.8% to 95.8%. DAS28 (CRP) with cut-off point for the remission of 2.3 underestimated disease activity by 45.8% compared with DAS28 (ESR). SDAI and CDAI showed agreement of 95.8%. The four indexes were associated with disease duration and HAQ. ConclusionsAlthough the activity indexes show good correlation, they show discrepancies in activity strata, thus requiring more researches to define a better index and better cut-off points.