A colonoscopy or sigmoidoscopy is a procedure used by doctors to investigate the internal cause of persistent symptoms like blood in the stool. These procedures allow specialists to visualize the intestinal lining to check for ulcers or other sources of bleeding. In some cases, a biopsy may be performed to rule out other medical conditions and confirm a diagnosis of CMPA. While the idea of these procedures is stressful for parents, they are valuable diagnostic tools that help provide clarity on your baby's health.