CRP and synovitis: ROC analysis showed a lower accuracy than calprotectin, with an AUC of 0.721 (95 % CI 0.612–0.829, p = 0.005) and a cut-off DAS28-CRP value of 1.61 (sensitivity 72 %, specificity 61 %, positive likelihood ratio 1.85, negative likelihood ratio 0.45), and it correctly classified PDUS synovitis in 66.3 % of patients.