CRP and Obesity: We compared the characteristics of patients that did not required necrosectomy (i.e. patients in which first step was effective versus those that underwent necrosectomy at step 2): among the following factors such as “SIRS, obesity, biliary AP, OF, size of the largest collection and CRP level” only OF before step-up approach (Fisher’s exact test – 17% versus 5% - p = 0.028) and the size of the collection (16.4 ± 3.8 cm versus 14 ± 2.9 – unpaired t test – p = 0.027) were statistically significant in the “step 2 group”.