Acute pancreatitis diagnosis requires two of three criteria per the revised Atlanta classification: (1) characteristic abdominal pain (acute onset, severe, epigastric, often radiating to the back, typically worse with eating and when supine, partially relieved by sitting forward), (2) serum lipase or amylase elevated to at least three times the upper limit of normal (lipase is preferred for its greater sensitivity and specificity, longer elevation window of 8-14 days versus 3-5 days for amylase, and fewer false-positive causes), and (3) characteristic findings on contrast-enhanced CT (pancreatic edema, peripancreatic fat stranding, pancreatic or peripancreatic fluid collections, or necrosis). CT is NOT required for diagnosis if the first two criteria are met and should be reserved for cases with diagnostic uncertainty or assessment of complications (typically performed 72-96 hours after onset to assess necrosis extent). The two most common etiologies are gallstones (40% -- stone passage through the common bile duct-pancreatic duct junction causing transient ampullary obstruction and reflux of bile into the pancreatic duct) and alcohol (30% -- direct toxic effect on acinar cells and increased pancreatic duct protein secretion causing...