Clinical disease activity index to measure RA

Allison Gandey

May 03, 2005

May 3, 2005

Vienna, Austria - Could a purely clinical score be a valid measure of rheumatoid arthritis (RA) disease activity? A study published in a recent issue of Arthritis Research & Therapy suggests the answer is yes. The findings demonstrate that acute-phase reactants (APRs) do not appear to contribute information to composite scores that is sufficiently important to change judgment of disease activity [ 1 ]. "Realizing there were several problems in daily practice with current measures, we found that we could develop a score that wouldn't require laboratory use, and this was the main trigger for our analysis," lead author Dr Daniel Aletaha (Medical University of Vienna, Austria) told rheuma wire . "Interestingly, we found that the impact of laboratory measures on current scores was actually very low."

The investigators anticipate that their clinical disease activity index (CDAI) will facilitate immediate and consistent treatment decisions and will help to improve patient outcomes long term. While a purely clinical score may have less utility in research, where APRs are almost always available, they expect the CDAI could have an important role in clinical practice.

We are not at all trying to claim that this is better than other scores. But what we are offering is a new tool to conduct assessments in different environments.

"With the CDAI, we don't have to wait for lab results that can take hours or a day, we have access to immediate results," Aletaha said. "We are not at all trying to claim that this is better than other scores. But what we are offering is a new tool to conduct assessments in different environments." Aletaha says he would like to see a shift in the management of RA. "Most diabetes patients know their blood glucose levels--the same thing can happen in RA."

Dr Josef Smolen

Working with senior author Dr Josef Smolen (University of Vienna, Austria and an editorial consultant for, the researchers hypothesized that APRs make limited contribution to the simplified disease activity index (SDAI). They also surmised that an SDAI modification eliminating APRs would have comparable validity in clinical cohorts. This SDAI modification, termed the clinical disease activity index, calculates the sum of tender and swollen joint counts (totaling 28 joints) and patient and physician global assessments.

The researchers used an observational cohort of 767 RA patients with an average disease duration of 8.1 +10.6 years and an independent inception cohort of 106 prospectively followed patients with a disease duration of 11.5 +12.5 weeks.

Easily calculated CDAI demonstrates similar validity to other composite indices

Aletaha and colleagues found that their clinically based hypothesis was statistically supported. APRs accounted for only 15% of the disease activity score (DAS) 28 and for 5% of the SDAI and the DAS28-C-reactive protein (DAS28-CRP). In both cohorts, the CDAI correlated strongly with DAS28 ( R=0.89-0.90) and comparably to the correlation of SDAI with DAS28 ( R=0.90-0.91).

In additional analyses, the researchers found that the CDAI, when compared with the SDAI and the DAS28, agreed with a weighted µ of 0.70 and 0.79. This was comparable to the agreement between DAS28 and DAS28-CRP.

The investigators found that all 3 scores correlated similarly with Health Assessment Questionnaire scores ( R=0.45-0.47). The average changes in all scores were greater in patients with better American College of Rheumatology response (p<0.0001 analysis of variance, discriminant validity). All scores showed similar correlations with radiological progression over 3 years ( R=0.54-0.58; p<0.0001).

"Our findings indicate that the CDAI--a composite score that employs only clinical variables and omits assessment of an APR--has similar validity to other currently employed composite indices for following patients with RA," the researchers write. "Also, using numerical summation, this score is very easy to calculate. For these reasons, the CDAI should facilitate decision making by physicians and avoid lags in efficient treatment adaptation for patients with RA."

For many rheumatologists, this lack of additional information provided by APR may be intriguing, because CRP and ESR are among the most commonly used laboratory tests in the evaluation of RA disease activity.

The investigators point out that all of the data obtained support their clinically derived hypothesis that APRs provide little information on actual disease activity on top of that provided by the combination of several clinical components. They note that this was the case for all analyzed RA activity scores despite the differences in their construction and component weighing. "For many rheumatologists, this lack of additional information provided by APR may be intriguing, because CRP and erythrocyte sedimentation rate are among the most commonly used laboratory tests in the evaluation of RA disease activity, and their importance as surrogates of the disease process as well as predictors of disease outcome are well recognized and irrefutable."

The researchers note that a limitation of the CDAI is that many physicians do not perform detailed joint counts. But they argue that joint counts are also required for other composite disease activity scores and the CDAI allows elimination of at least 1 variable that is frequently missed at patient visits--the APR.

However, the research team urges physicians to continue regularly obtaining an APR measure during follow-up because, like the CDAI, it reflects disease activity and correlates with long-term outcome. They note that the APR can be employed as an independent measure as well as being a part of a composite index.

"Of course, further validation of the CDAI will be required to fully confirm its value. Such additional investigations should include analyses of construct validity with regard to radiographic damage and predictive value with regard to long-term functional outcome in larger cohorts of patients," Aletaha and colleagues write. "In addition, cutoffs for disease activity categories, including remission, as well as changes that reflect important responses must be determined. Such analyses are currently under way."



1. Aletaha D, Nell VPK, Stamm T, et al. Acute phase reactants add little to composite disease activity indices for rheumatoid arthritis: validation of a clinical activity score. Arthritis Res Ther 2005; 7:R796-R806. Available at:


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