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Estimated Cutoff Points for the 28-Joint Disease Activity Score Based on C-reactive Protein in a Longitudinal Register of Early Arthritis

Objective. To estimate the cutoff points for the 28-joint Disease Activity Score (DAS28) calculated using C-reactive protein (CRP) measurements from patients with early arthritis. Methods. We analyzed data from 568 visits of 207 patients enrolled in our prospective longitudinal register of early arthritis. Six rheumatologists evaluated the degree of disease activity at each visit on the basis of the available clinical data, and the final degree of disease activity was established by consensus. DAS28 values were calculated for each visit using CRP or erythrocyte sedimentation rate (ESR). Through a ROC analysis, cutoff points for both indices, as well as for minimal disease activity (MDA), were selected on the basis of the best tradeoff values between sensitivity and specificity. Results. The cutoff values to classify disease activity with the DAS28-CRP were 2.3, 3.8, and 4.9, considering remission at < 2.3, low disease activity 2.3–3.8, moderate disease activity 3.8–4.9, and high disease activity > 4.9. The cutoff value for MDA when calculated with CRP was 2.6. The area under the ROC curves was always greater for DAS28-CRP than for DAS28-ESR, reaching statistical significance for low/moderate activity and for the MDA. Conclusion. Our study confirms that the cutoff points for DAS28-CRP are lower than those described for DAS28-ESR, suggesting that DAS28-CRP may be more accurate to assess disease activity in our population.