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Blood in poo: Causes and diagnosis

Blood in poo, or stool as doctors may call it, can be frightening if it is discovered while wiping after going to the toilet.

Never ignore blood in poo. Although it may not be a sign of something serious, it can be a symptom of some serious medical conditions.

Here's what you need to know about the possible causes of bloody poo and what you - and your doctor - should do if you discover a problem.

Causes of blood in poo

Blood in poo means there is bleeding somewhere in your digestive tract. Sometimes the amount of blood is so small that it can only be detected by a faecal occult test, a test to check for hidden blood in the poo.  At other times it may be visible on toilet paper or appear in the toilet after a bowel movement as bright red blood. Bleeding that occurs higher up in the digestive tract may make poo appear black and tarry.

Possible causes of blood in poo include:

Diverticular disease. Diverticula are small pouches that project from the colon wall. Usually diverticula don't cause problems, but sometimes they can bleed or become infected.

Anal fissure. A small cut or tear in the tissue lining the anus, similar to the cracks that occur in chapped lips or a paper cut. Fissures are often caused by passing a large, hard stool and can be painful.

Colitis. Inflammation of the colon. Among the more common causes are infections or inflammatory bowel disease.

Angiodysplasia. A condition in which fragile, abnormal blood vessels lead to bleeding.

Peptic ulcers. An open sore in the lining of the stomach or duodenum - the upper end of the small intestine.  Many peptic ulcers are caused by infection with a bacterium called Helicobacter pylori (H. pylori). Long-term use or high doses of anti-inflammatory drugs such as aspirin, ibuprofen and naproxen can also cause ulcers.

Gastroenteritis. A viral or bacterial infection of the stomach and bowel, which your immune system will usually fight off after a few days. It can cause diarrhoea that contains traces of blood and mucous, as well as other symptoms such as vomiting and stomach cramps.

Polyps or cancer. Polyps are benign growths that can grow, bleed and become cancerous. More than 40,000 people are diagnosed with bowel cancer in the UK each year. It often causes bleeding that is not noticeable with the naked eye.

Oesophageal problems. Varices of the oesophagus or tears in the oesophagus can lead to severe blood loss.

Blood in poo diagnosis

It is important to get a doctor to evaluate any blood in the poo.  Any details you can give about the bleeding will help your doctor locate the site of the bleeding. For example, a black, tarry stool is more likely to be caused by a peptic ulcer or other problem in the upper part of the digestive tract. Bright red blood, or maroon-coloured stools, usually indicate a problem in the lower part of the digestive tract, such as haemorrhoids or diverticulitis.

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