Red flags Diagnostic testing should be more intensive when the following red flags are present either at initial presentation or at any time after diagnosis: Older age Weight loss Rectal bleeding Iron deficiency anemia Family history of colon cancer, inflammatory bowel disease, or celiac disease Nocturnal diarrhea Differential diagnosis Because patients with IBS can develop organic conditions, testing for other conditions should also be considered in patients who have red flags or develop markedly different symptoms during the course of IBS.