Blood in the stool: these are the potential causes


Blood in the stool, also known as haematochezia, is not necessarily indicative of a malignant disease. As Professor Antonio Nocito from the Stomach Centre at the Cantonal Hospital Baden advises, the causes should always be clarified by a doctor.

When is blood in the stools dangerous?

As a rule, the causes of blood in the stools are comparatively harmless but they can also be an indication of a serious disease in the gastrointestinal tract. In any case, it is advisable to consult a doctor, especially if the stools contain blood for several days.

Light blood, dark blood – what does this mean?

When the source of the bleeding is located further down the intestinal tract, i.e. in the anal canal or in the lower colon, the colour is usually light (haematochezia). If the source is in the upper regions of the tract, the blood is often dark in colour because the red colouring is broken down by bacteria on the way to being excreted (melaena). But the speed of flow also has an influence: if the blood flows quickly, it may well be light in colour when excreted with the stools, even if it stems from the upper section. Dark-coloured blood usually means that the stools are dark too. However, stools can become black in colour after consuming dark chocolate, beetroot, spinach or iron supplements.

Blood in the stool should always be checked by a doctor, especially if the stools contain blood for several days.
Prof. Dr. med. Antonio Nocito, Director of the Department of Surgery at the Cantonal Hospital Baden

So whether the blood in the stool is light or dark says nothing about the malignancy of the disease?

Not necessarily. Bright-coloured blood can indicate polyps, for example, which are benign growths inside the colon that begin to bleed when they reach a certain size. These are mostly painless. The polyps should be surgically removed so that they don’t develop into colon cancer. Light-coloured blood can also be an indication of tumours in the stomach or small intestine, although these are not necessarily malignant.

Dark blood in the stools

Black blood may be a bacterial infection in the stomach or duodenum, which can usually be treated with medication. Sometimes, however, chronic inflammatory bowel diseases such as ulcerative colitis or Crohn's disease are the cause. In this case, a gastroscopy or a colonoscopy, i.e. tissue samples, will provide clarification.

What is occult blood?

Sometimes minute bleeding in the stomach or intestines mixes with the stool, which cannot be seen with the naked eye. However, the blood (also called invisible or occult blood) can be detected with special test procedures, for example the haemoccult test. These tests are conducted in cases that include suspected colon cancer.

What does light-coloured blood on the toilet paper indicate?

This is probably due to haemorrhoids, which are harmless but can be very painful. These occur when the mucosa that pads the anal canal ruptures and bleeds. Fine tears, or fissures, in the intestinal mucosa can also lead to bleeding. The most common cause of haemorrhoids and fissures is heavy straining when passing stools as a result of constipation. A change to the diet is often all that's needed to solve the problem.

How can bloody stools be prevented?

Although there is no patent remedy to guarantee prevention, there are ways to reduce the risk of gastrointestinal diseases. A balanced, high-fibre diet and sufficient fluids can help prevent the formation of particularly hard stools and excess stomach acid. Regular exercise also helps keep constipation at bay. It goes without saying that excessive alcohol consumption is damaging. Last but not least: schedule regular screenings for colorectal cancer.


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