Explore a comprehensive lecture on gastrointestinal (GI) conditions, covering organic and functional disorders. Learn about the importance of laboratory investigations in prioritizing patients for invasive GI tests and their role in diagnosis, disease management, and treatment monitoring. Delve into topics such as the gastrointestinal system, stomach disorders, Helicobacter Pylori testing, gastrinoma, faecal fat collection, exocrine pancreatic function tests, bile acid diarrhoea, protein digestion, coeliac disease and testing, large intestine disorders, calprotectin clinical utility and laboratory aspects, colorectal cancer screening methods including guaiac faecal occult blood testing and faecal immunochemical testing (FIT). Examine a case history of a 51-year-old male patient to apply the knowledge gained throughout the lecture.