Blood in Stool

Why Do I Have Bloody Stool?

Blood in stool can occur for many different reasons. While some cases that only last a couple of days may not mean that the person has an underlying condition, it’s important to track changes in your bowel habits and see a doctor if rectal bleeding persists for more than a week or so. The medical condition is technically called hematochezia and is not always easily detected because blood that has passed through large portions of the gastrointestinal tract (GI tract) can darken and simply make the stool look blackish in color.

How much a person bleeds varies widely depending on the case, ranging from a few drops that may or may not be noticed when the blood blends with feces to a significant amount of blood that can cause a person to feel dizzy or weak as a result of decreased blood pressure. In the most extreme cases, severe blood loss will result in bodily shock.

Where Does the Blood in my Stool Come From?

Blood in stool most likely originates in a patient’s colorectal region, which includes the large intestine (colon), rectum and anus. This is the area of the body where stools are formed, after fluid and nutrients are absorbed by the rest of the GI tract. The color of any blood that is expelled from the body in stool can vary and indicate how far up the large intestine the source of bleeding as located. For example, bright red blood in the stool probably means that the bleeding is coming from the lower part of the colon (the sigmoid colon), the rectum and the anus. Conversely, darker blood—which can sometimes look sticky and black—most likely comes from a source higher up in the colon or even higher in the GI tract such as the stomach or small bowel. Tests such as fecal occult blood testing and fecal immunochemical testing are available to test for hidden blood in a patient’s feces.

What Causes Blood in Stool?

A variety of GI diseases and conditions can result in rectal bleeding. The most common are tears in the anus (anal fissure), hemorrhoids, colon pouches (diverticula), colitis, proctitis and ulcerative colitis. Blood in stool is also a symptom of colon cancer, so it’s important to follow up with a professional if the blood doesn’t go away. Dark black blood or melena in the stool can be a sign of bleeding from the upper GI tract, which can come from peptic ulcer disease or tumors of the stomach/small bowel.  Depending on the reason for bleeding, many different treatment options may be necessary.

Most of these conditions can be diagnosed after a routine exam such as colonoscopy or EGD. Other times, if the source of bleeding is located in the upper GI tract—esophagus, stomach and small intestine—an endoscopy procedure such as EGD can also be useful for diagnosis. Contact a gastroenterologist if you have blood stool and think you may need treatment.


Reviewed 12/29/2011 by David M. Nolan, M.D.
Diplomate of the American Board of Internal Medicine, 2011
Currently a Fellow of Gastroenterology, at UCI 2011-2014