Thank you for your query. Would you please clarify a few things for me? 1)how old is your friend? Any history of smoking or excessive alcohol consumption? 2) any history or chronic vomiting? 3)any family history of cancer/autoimmune disease /inflammatory bowel disease? 4)any history of liver disease? 5)any bleeding or clotting issues? Blood in stools and vomitus is usually caused an lesion /erosion anywhere in the gastrointestinal tract (esophagus, stomach, small and large intestine). Peptic ulcers, duodenal ulcers, intestinal polyps, esophageal varices (erosions in the esophagus), tumors, hemorrhoids can all cause bleeding. A colonoscopy or endoscopy visualizes different parts of the tract to look for these lesions. Certain areas of the intestine, however, may not be covered during this exam and hence may account for a negative test in the presence of Frank bleeding. She may need more testing, hospitalization, and transfusions if the bleeding is too much and the cause of the bleed identified promptly. Hope I ve answered your questions. Please get back to us if you have further questions. Wish you both good health