Gastrointestinal Tract

All relevant functional tests are explained with a detailed presentation of indications, contraindications, side effects, test preparation, framework conditions, concrete instructions for the actual test execution, and the interpretation of test results. Specific normal ranges and cut-off values are always provided, even for special situations (gender, age, BMI, puberty phases, cycle phases, acute illnesses, medications, etc.). A special feature is the emphasis on test preparation, execution, and interpretation, as well as the interdisciplinary nature. Gastrointestinal hormones and peptides such as gastrin, serotonin, VIP, glucagon, somatostatin, or PP are crucial in neuroendocrine tumors, carcinoids, or GEP-NET tumors. In addition to basal values, the secretin test plays an important role. The intra-arterial calcium stimulation test in insulinoma diagnostics is explained.