Healthy Living

Blood in Your Stool: Where Does It Come From?

Blood in Your Stool: Where Does It Come From?

Where does the bleeding come from?

Bleeding that causes blood in the stool can develop in any part of the gastrointestinal tract.

  • Bleeding from the rectum or anus – the blood is usually bright red and is fresh. The blood may not be mixed with the stool, but the blood may be noticed after passing stools. In some cases, streaks of blood cover the stools. Conditions such as hemorrhoids and anal fissure are some examples.
  • Bleeding from the colon – when bleeding comes from the colon, most of the time, the blood is mixed with the stool. The color of the blood is dark red, which occurs in diverticular disease, colitis, or a tumor in the bowel. However, there are instances where bleeding is brisk and is not mixed with the stool. A sudden bleed caused by the diverticula is a good example.
  • Bleeding from the small intestine or stomach – since the blood is coming from a higher region, it has to travel to the entire gastrointestinal tract. Thus, the blood is altered, becomes dark, and mixes with the stool. As a result, the stool becomes plum in color or black (melena). This occurs when there are stomach bleeding and duodenal ulcer. Melena indicates that there is a lot of bleeding coming from the duodenum or stomach. This type of rectal bleeding is a medical emergency. 

What are the tests to be performed?

The tests that are needed will depend on the possible cause of blood in the stool. It will be decided by the doctor based on the patient’s medical history and physical examination. The following tests are usually recommended to determine the cause of bleeding:


Colonoscopy is a test where a healthcare professional, usually a doctor or a nurse, looks into the colon. The patient is not put to sleep during the procedure. However, a sedative is given to make the patient drowsy.

During colonoscopy, a colonoscope is used. It is a thin and flexible telescope, about as thick as the little finger. The colonoscope is passed via the anus and into the colon. It can be pushed further as far as the cecum – the area where the large intestine and small intestine meet. In addition, the colonoscope has a side channel where devices can pass through. For example, a small tissue sample may be taken from the colon through the use of an instrument that is passed on the side channel.


Sigmoidoscopy is a procedure that uses a sigmoidoscope – a small telescope with a light source attached to its end. The sigmoidoscope is almost similar to a colonoscope, but the former is much shorter. 

Sigmoidoscopy is easier to perform than a colonoscopy. If bleeding is assumed to be coming from the rectum or lower colon, it is better to do a sigmoidoscopy than colonoscopy. The doctor inserts the sigmoidoscope into the anus then slowly pushes into the rectum up to the sigmoid colon. Doing so allows the doctor to look into the lining of the sigmoid colon and rectum. Sigmoidoscopy may be uncomfortable but is not usually painful.

Virtual Colonoscopy

A virtual colonoscopy, also referred to as CT colonography, is a new diagnostic test that allows the doctor to have a good look of the colon without passing a tube inside of it. The tube is only passed into the rectum and does not need to go up further. When the tube is already inside, a gas is pushed into the bowel for it to open. Then, a CT scan of the bowel is done.

Virtual colonoscopy is usually recommended to people who are frail and who cannot tolerate colonoscopy. It is less uncomfortable and is better tolerated than colonoscopy. However, it is not yet available in many areas. 

Key Takeaways

  • The blood caused by bleeding from the rectum or anus is usually fresh and bright red.
  • If the bleeding comes from the colon, the blood is mixed with the stool.
  • Melena is a plum-colored or black stool.