What Can Cause Blood in Poo? (Stool)

Blood in the stool may be noticed after a bowel movement or following a test arranged by a doctor. It denotes the presence of bleeding somewhere within the gastrointestinal tract, comprising the mouth, esophagus, stomach, small intestine, large intestine and anus.

The amount of blood in the stool may be so small that it is only detected by a fecal occult test, which looks for non-visible blood in the stool. If more blood is present, it may be noticed on toilet tissue or seen as bright red blood in the stool after a bowel movement.

Bleeding from the gut may make the stool look black and tarry, which is referred to as melena. Bright red blood is referred to as hematochezia. Melena is more likely to occur when the blood originates in the esophagus, stomach or small intestine, while hematochezia is more likely when the source is the large intestine or rectum.

Some of the most common causes of gastrointestinal bleeding and blood in the stool are described below.

Diverticular Disease

Here, small pouches or pockets called diverticula develop in and project from the intestinal lining. They are common in older individuals and are thought to form as the result of weakening of the colonic wall over time as hard stools are passed through it. Diverticular disease does not usually cause symptoms, but the diverticula sometimes become infected or bleed. Approximately 15% of individuals with this disease find that they pass blood in their stool. However, the problem does not usually cause pain and it is self-limited in around 80% of cases. Bleeding that does not clear up may require hospital monitoring and blood transfusion.

Anal Fissure

This is a small tear or cut in the thin, moist lining of the anus, often as a result of passing a hard and/or large stool. This can cause pain and bleeding. The majority of anal fissures resolve without treatment, especially if simple changes are made such as an increased intake of dietary fiber, although medication or surgery is occasionally required.

Ulcerative Colitis

Ulcerative colitis is an inflammatory bowel disease characterized by chronic inflammation and ulceration of the innermost lining of the colon and rectum. Symptoms develop gradually, but the condition can be debilitating or even life-threatening. No cure has yet been developed, but treatment is often effective in improving symptoms.

Angiodysplasia of the Colon

This condition is characterized by alteration in the aging blood vessels in the colon, which become fragile, swell and break, resulting in bleeding. The bleeding may be slow, eventually causing anemia, or it may be severe and require hospital monitoring and blood transfusion.

Peptic Ulcers

A peptic ulcer is a sore found in the stomach or duodenum. It is often the result of infection by the organism Helicobacter pylori, or the ongoing use of anti-inflammatory drugs such as ibuprofen and aspirin. The most common symptom is stomach pain, which may be exacerbated by stress or eating spicy food.

Colon Polyps and Colorectal Cancer

Polyps are small growths that form on the colon lining. They are usually benign, but can increase in size, start to bleed and potentially become cancerous, leading to colon cancer. This can be fatal if the cancer is not discovered until it is advanced. Rectal cancer is cancer that arises in the last section of the colon. Colon and rectal cancers are together referred to as colorectal cancers. Anyone can develop colon polyps, although people aged 50 years and older are at an increased risk, along with people who smoke, are overweight, or have a family history of colon polyps or colon cancer.

Colorectal cancer often causes bleeding that cannot be seen with the naked eye. It is therefore important that regular screening for this disease be done, since polyps found early on in the course of disease can usually be removed so that cancer is prevented from developing in a number of cases.


Further Reading

Last Updated: Feb 26, 2019

Sally Robertson

Written by

Sally Robertson

Sally has a Bachelor's Degree in Biomedical Sciences (B.Sc.). She is a specialist in reviewing and summarising the latest findings across all areas of medicine covered in major, high-impact, world-leading international medical journals, international press conferences and bulletins from governmental agencies and regulatory bodies. At News-Medical, Sally generates daily news features, life science articles and interview coverage.


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