The goal of this retrospective observational study is to construct a composite outcome to measure the success of treatment in patients who are presenting with acute cholangitis (blockage and infection of bile ducts) and undergoing a drainage procedure with different modalities. The study is not intended to test any predetermined hypothesis and does not have any comparison group. The participants' data are collated from retrospective hospital records and analysed for the purpose of the study. All the procedures are in place to ensure the confidentiality of the study participants while collating, analysing and sharing study findings.

Study Aim To develop and internally validate a Composite Index that summarizes overall outcome burden in patients with acute cholangitis.

Primary Objective (Index Development)

1. To derive a Multidimensional Composite Index for Outcome Burden among patients with acute Cholangitis undergoing Biliary Drainage, that inegrates

• Mortality (30-day and in-hospital)
• Organ support,
• ICU admission and ICU length of stay,
• Complication burden and severity (AGREE and Clavien-Dindo classification as applicable),
• Hospital length of stay,
• 30-day reintervention
• 30-day readmission.

Secondary Objectives

1. To evaluate the association of the Composite Index with:

   • TG18 severity grade (I vs II vs III),
   • Baseline physiological/lab derangement (WBC, bilirubin, creatinine, lactate),

2. To explore whether timing of biliary drainage is associated with composite index scores (exploratory-hypothesis-generating).

Inclusion Criteria

• Age 18 to 80 years
• Hospital admission with definite diagnosis of acute cholangitis meeting TG18 diagnostic criteria
• TG18 Grade I (Mild) Grade II (moderate) or Grade III (severe) at presentation/admission or prior to drainage.
• Underwent biliary drainage attempt (ERCP/PTBD/EUS-BD) or were planned for drainage (including failures with rescue drainage).
• First episode of index BD in case of patients undergoing multiple episodes of index BD as per operational definitions (Technical supplement 1)
• Planned repeat BD in same admission shall be considered as continuation of the index BD and all the procedural details shall be documented and analysed.

Exclusion Criteria

• Pregnant women
• Missing key outcome data (minimum required: mortality status + ICU admission status + Length of stay)
• Non-biliary sepsis without evidence of biliary obstruction/infection on review.
• A patients with past history of BD outside the study setting (As this is akin to second episode of Index BD)
• Subsequent episodes of Index BD (other than the first index BD episode) among patients with more than one episode of Index BD.

Study Population

• Age 18 to 80 years
• Hospital admission with definite diagnosis of acute cholangitis meeting TG18 diagnostic criteria
• TG18 Grade I (Mild), Grade II (moderate) or Grade III (severe) at presentation/admission or prior to drainage.
• Underwent biliary drainage attempt (ERCP/PTBD/EUS-BD) or were planned for drainage (including failures with rescue drainage).
• First episode of index BD in case of patients undergoing multiple episodes of index BD as per operational definitions (Technical supplement 1).
• Planned repeat BD in same admission shall be considered as continuation of the index BD and all the procedural details shall be documented and analysed.