Diagnosis of Lynch Syndrome Detailed family history Clinical criteria followed by testing for microsatellite instability (MSI) or with immunohistochemistry (IHC) Genetic testing for confirmation (See also the 2015 American Gastroenterological Association's guideline regarding diagnosis and management of Lynch syndrome and the American College of Gastroenterology's clinical guideline on the genetic testing and management of hereditary gastrointestinal cancer syndromes.)