Discriminating ability of composite indices for measuring disease activityin rheumatoid arthritis: a comparison of the Chronic Arthritis Systemic Index, Disease Activity Score and Thompson's articular index

Objective. To compare the discriminating ability of the chronic arthritis s ystemic index (CASI), an index that uses the Health Assessment Questionnair e (HAQ) as the main variable, with the disease activity score (DBS) and Tho mpson's articular index (TAI) to detect high and low disease activity in rh eumatoid arthritis (RA). Methods. Two hundred and two RA patients were examined. According to criter ia proposed previously, they were divided into two subgroups: these with ac tive disease and those with low activity. The areas under receiver operatin g characteristic (ROC) curves were employed to assess the diagnostic accura cy of the CASI in comparison with the DAS and TAI for the discrimination of disease activity. Results. The difference between areas under the ROC curves of the CASI and TAI (0.897 +/- 0.023 vs 0.780 +/- 0.032) and between the DAS and TAI (0.933 +/- 0.018 vs 0.780 +/- 0.032) was highly significant (P = 0.0001), thus re flecting the accuracy of the diagnostic assessment. No difference arose bet ween areas under the ROC curves of the CASI and the DAS (difference between areas = 0.036 +/- 0.022; P = 0.103). Conclusion. The CASI discriminates just as well between high and low diseas e activity as does the DAS. Either index consisting of more than one variab le performs better than TAI. We conclude that even including the HAQ, a sev erity parameter in the long term, it is possible to construct an index that , at any time point, evaluates disease activity as well.