AbstractBackground/PurposeThe aim of this study was to clarify the clinical characteristics of acute cholangitis (AC) after bilioenteric anastomosis and stent‐related AC in a multi‐institutional retrospective study, and validate the TG18 diagnostic performance for various type of cholangitis.MethodsWe retrospectively reviewed 1079 AC patients during 2020, at 16 Tokyo Guidelines 18 (TG 18) Core Meeting institutions. Of these, the post‐biliary reconstruction associated AC (PBR‐AC), stent‐associated AC (S‐AC) and common AC (C‐AC) were 228, 307, and 544, respectively. The characteristics of each AC were compared, and the TG18 diagnostic performance of each was evaluated.ResultsThe PBR‐AC group showed significantly milder biliary stasis compared to the C‐AC group. Using TG18 criteria, definitive diagnosis rate in the PBR‐AC group was significantly lower than that in the C‐AC group (59.6% vs. 79.6%, p < .001) because of significantly lower prevalence of TG 18 imaging findings and milder bile stasis. In the S‐AC group, the bile stasis was also milder, but definitive‐diagnostic rate was significantly higher (95.1%) compared to the C‐AC group. The incidence of transient hepatic attenuation difference (THAD) and pneumobilia were more frequent in PBR‐AC than that in C‐AC. The definitive‐diagnostic rate of PBR‐AC (59.6%–78.1%) and total cohort (79.6%–85.3%) were significantly improved when newly adding these items to TG18 diagnostic imaging findings.ConclusionsThe diagnostic rate of PBR‐AC using TG18 is low, but adding THAD and pneumobilia to TG imaging criteria may improve TG diagnostic performance.