The BISAP (Bedside Index for Severity in Acute Pancreatitis) was developed by Wu and colleagues in 2008 from a retrospective analysis of over 18,000 pancreatitis admissions from a national US database. It was specifically designed to be a simple 5-point bedside tool that could predict in-hospital mortality within 24 hours of admission — before CT imaging or 48-hour Ranson's criteria become available. BISAP was validated in a separate cohort of over 16,000 patients, demonstrating comparable discriminatory ability to APACHE-II while being far simpler to calculate. Each point of BISAP approximately doubles mortality risk.