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Abstract
Background Recently, ASDAS has been developed as a disease activity measuring tool for ankylosing spondylitis, using a similar methodology to that used for the development of the Disease Activity Score (DAS) in rheumatoid arthritis. Two versions of ASDAS have been proposed, one based on CRP (preferred) and the other based on ESR (alternative), much like the two versions of DAS28. In the light of some recent reports showing substantial difference between the two versions of DAS28 in classifying RA patients into categories of disease activity (1), it is of interest to assess the agreement between the two ASDAS versions at individual level.
Objectives To assess the agreement between the ESR- and CRP-based ASDAS scores in AS patients.
Methods Data were obtained from the local clinical database which contains slightly over 500 AS patients. Patients with full data at baseline were included in this analysis. Mean ASDAS-ESR and ASDAS-CRP values were compared by Spearman correlation and scatter plot with linear regression analysis. Bland–Altman plots were generated for assessment of the variation between ASDAS-CRP and ASDAS-ESR. Percent agreement, kappa statistic, and weighted kappa statistic weredetermined for the two definitions.
Results 396 patients (291 M; 44 ±12.0) were identified with complete data at baseline for this analysis. Mean disease duration was 9.4 ± 8.2. Mean BASDAI, BASFI and BASMI scores were 3.6 ± 2.3, 2.9 ± 2.6, 3.9 ± 1.9, respectively. HLA B27 was positive in 65% of the tested patients. 83.7% of the patients were using NSAID and 20.7% of patients were using anti TNF agents. Mean ASDAS scores based on CRP and ESR were very similar (2.9 ± 1.1 vs 2.8 ± 1.0). There was a strong correlation between the two by Spearman’s test (r=0.9, p<0.001) and linear regression (R²=0.82, p<0.001). Between the two methods; the agreement rate, kappa and weighted kappa values were%70, 0.56 and 0.76 respectively. The corresponding values for females were 63.2%, 0.44, and 0.67 and for males 73.7%, 0.61, 0.80, respectively. Bland-Altman analysis showed excellent agreement between the two scores (ASDAS-CRP –ASDAS-ESR) with a mean difference of −0.0 ± 0.48 (95% CI −0.04, −0.047). Upper and lower limits of agreement were 0.95 (95% CI 0.87, 1.03) and −0.95 (95% CI −1.03, −0.87), respectively. Mean difference was 0.20 ± 0.49 in females and -0.10 ± 0.44 in males.
Conclusions Although similar number of patients can be classified into the defined categories of disease activity with ASDAS-CRP and ASDAS-ESR, a small number of patients in each category can be classified into different categories with different ASDAS versions. After all, the results suggest a good agreement, particularly in males, between ASDAS-ESR and ASDAS-CRP.
References
Hensor EM, Emery P, Bingham SJ, Conaghan PG, Consortium Y. Discrepancies in categorizing rheumatoid arthritis patients by DAS-28(ESR) and DAS-28(CRP): can they be reduced? Rheumatology. 2010 Aug;49(8):1521-9.
Disclosure of Interest None Declared