Blood in stool is very frequent but at some time may be invisible to the naked eye in which case it is called occult. However, it is most often seen as clear bright red spot mostly on the toilet paper, it can also be maroon in colour, black and tarry. Causes of blood in stool range from harmless conditions of the gastrointestinal tract such as haemorrhoids to serious conditions such as cancer. Frequent and repetitive blood in the stool should be evaluated by a healthcare professional in all cases.
Massive rectal bleeding (known medically as haematochezia) refers to passage of bright red blood from the anus, often mixed with stool and/or blood clots. Most rectal bleeding comes from the colon, rectum, or anus. The colour of the blood during rectal bleeding often depends on the location of the bleeding in the gastrointestinal tract. Generally, the closer the bleeding site is to the anus, a brighter red the blood will be. Thus, bleeding from the anus, rectum, and the sigmoid colon tend to be bright red, whereas higher (orally) bleeding from the transverse colon and the right colon (transverse and right colon are several feet away from the anus) tend to be dark red or maroon coloured.
In some cases bleeding can be black and “tarry” (sticky) and foul smelling. The black, smelly and tarry stool is called melena. Melena occurs when the blood has been in contact with gastric acid or has been in the colon long enough for the bacteria to break it down into chemicals (haematin) that are black. Therefore, melena usually signifies bleeding is from the upper gastrointestinal tract (for example: bleeding from ulcers in the stomach or the duodenum or from the small intestine) because the blood usually is in the gastrointestinal tract for a longer period of time before it exits the body. Sometimes melena may occur with bleeding from the right colon.
Blood from the sigmoid colon and the rectum usually does not stay in the colon long enough for the bacteria to turn it black. Rarely, massive bleeding from the right colon, from the small intestine, or from ulcers of the stomach or duodenal can cause rapid transit of the blood through the gastrointestinal tract and result in bright red rectal bleeding. In these situations, the blood is moving through the colon so rapidly that there is not enough time for the bacteria to turn the blood black.
Sometimes, bleeding from the gastrointestinal tract can be too slow to cause either rectal bleeding or melena. In these patients bleeding is occult (not visible to the naked eyes). The blood is found only by testing the stool for blood (faecal occult blood testing) in the laboratory. Occult bleeding has many of the same causes as rectal bleeding and may result in the same symptoms as rectal bleeding. It is often associated with anaemia that is due to loss of iron along with the blood (iron deficiency anaemia). For more information, please see the colon cancer screening and faecal occult blood test articles.
Definition of Bloody or tarry stools:
The presence of blood in the stools is frequent and indicates some sort of injury or bleeding disorder in the digestive tract. The amount of bleeding gives often a clue as to the origin. Your doctor may use the term “maelena” to describe black, tarry, and foul-smelling stools (black tar= maelena) or “haematochezia” to describe bright red- or maroon-coloured (fresh) stools.
Blood in the stool may come from anywhere along your digestive tract, from mouth to anus. It may be present in such small amounts that you cannot actually see it, but is only detectable by a faecal occult blood test. When there IS enough blood to change the appearance of your stools, the doctor will want to know the exact colour to help find the site of bleeding. To make a diagnosis, your doctor may use endoscopy or special x-ray studies.
A black stool usually means that the blood is coming from the upper part of the gastrointestinal (GI) tract and was broken down by the gastric acid. Blood will typically look like tar after it has been exposed to the body’s digestive juices. Stomach ulcers caused by ibuprofen, naproxen, or aspirin are common causes of upper GI bleeding.
Maroon-coloured stools or bright red blood usually suggest that the blood is coming from the lower part of the GI tract (large bowel or rectum). Haemorrhoids and diverticulitis (inflammation of an abnormal pouch in the colon) are the most common causes of lower GI bleeding. However, sometimes massive or rapid bleeding in the stomach causes bright red stools.
Consuming black liquorice, lead, iron pills, bismuth medicines or blueberries can also cause black stools. Beets and tomatoes can sometimes make stools appear reddish. In these cases, your doctor can test the stool with a chemical to rule out the presence of blood.
Brisk bleeding in the oesophagus or stomach (such as with peptic ulcer disease), can also cause you to vomit blood.
Upper GI tract (usually black stools):
Lower GI tract (usually maroon or bright red, bloody stools):