title: Ruling in or out a source of gastrointestinal bleeding.
abstract: OBJECTIVE
  The search for a source of gastrointestinal bleeding is associated with two distinct approaches of trying to rule in a specific diagnosis or rule out any potential source of bleeding. The study aim was to understand the conceptual differences underlying the two searches.
  
  
  METHODS
  The performance of endoscopy as diagnostic test is analyzed in terms of Bayes' formula.
  
  
  RESULTS
  The performance of gastrointestinal endoscopy to rule in a suspected lesion is mostly influenced by its underlying specificity. Because the specificity of endoscopy is less likely to be affected by procedural exigencies, the demands on pre-procedural prep and general quality can be more relaxed. In contradistinction, the performance of endoscopy to rule out a suspected bleeding site is mostly influenced by its sensitivity, which can easily be compromised by suboptimal procedural conditions.
  
  
  CONCLUSIONS
  Paradoxically, the more urgent, focused, and important search (to rule in a bleeding site), carries less stringent criteria for its execution than the more general and aimless search (to rule out a bleeding site) that frequently ends up just empty handed.
authors.affiliation: The Portland VA Medical Center and the Division of Gastroenterology/Hepatology, Oregon Health & Science University, Portland, USA.
authors.forename: Amnon
authors.initials: A
authors.lastname: Sonnenberg
keywords: Bayes’ formula; gastrointestinal bleeding; gastrointestinal endoscopy; medical decision analysis; outcome research