CRP and abscess: In the internal validation, the AUCs of high CRP (0.70, 95 % CI 0.66–0.75), large abscess diameter (0.68, 95 % CI 0.44–0.91), RPE (0.73, 95 % CI 0.60–0.85), and risk score (0.83, 95 % CI 0.69–0.96) were comparable to those from the initial ROC analysis.