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Blood in the stool

Written by Caidr's team of doctors and pharmacists based in UK | Updated: 26.01.2023 | 3 min read

Blood in the stool, or rectal bleeding, is where blood is found coming from the back passage. You may notice this mixed in with the stool or after passing stool, either on the tissue or in the toilet. It’s important to seek medical attention, as this indicates that some part of the gut is bleeding.

The stool may be different colours. If it is bright red, it usually indicates a bleed towards the end of the intestine, either from the colon or rectum. Darker red stool indicates that there may be bleeding higher up in the gut, in the lower small intestine. Black, tarry schools indicate bleeding from much higher up, from the stomach or upper small intestine.

What are the causes of rectal bleeding?

Bright red blood can be caused by a haemorrhoid or a tear in the anus called an anal fissure. These are most often caused by straining from constipation. If you are on medications that thin the blood, like warfarin or aspirin, this can increase your likelihood of bleeding.

Anal sex can cause trauma that leads to bleeding from the back passage, and sexually transmitted infections from anal sex may also be responsible.

Blood that is mixed in with the poo is caused from issues higher up in the gut. Examples include inflammatory bowel diseases like ulcerative colitis or Crohn’s disease, tummy bugs or anal fistulas.

Blood mixed in with stool can also be a worrying sign of bowel cancer, which is common but more likely in those with a history or family history of colon polyps, or those older than 65 years old.

Dark poo can look black and can be caused by certain foods or medications like iron tablets. Eating beetroot can cause stool to look red, purple or a dark blackish colour.

There are more worrying causes of dark black poo, such as bleeding in the stomach or small intestine from a stomach ulcer, diverticulitis, or blood-thinning medications like warfarin.

When should I see my doctor?

If you experience bleeding from the back passage and you can’t identify a cause, such as haemorrhoids that you feel confident treating at home, you should book an appointment with your doctor.

They will ask about your symptoms and family history, about certain lifestyle factors like smoking, alcohol intake and diet, and they will examine your abdomen. With your permission, they will also likely do an intimate examination of your back passage.

Blood tests will be important to look for signs of anaemia or infection. Stool samples can be sent off to look for blood in the stool and can help identify any infections that may be present, or to look for evidence of any inflammation. Further investigations may be required such as procedures like colonoscopy or imaging such as a CT scan.

When should I seek a doctor urgently?

Rectal bleeding may be associated with rectal pain or abdominal pain or cramping.

Urgent medical advice is required for significant loss of blood that leads to dizziness, tiredness, rapid breathing, confusion or fainting.

Additionally, if the rectal bleeding doesn’t stop, if there is severe anal pain or you are also vomiting blood, then you should seek urgent medical attention.

If your symptoms are not improving on their own or with medication from your pharmacy, you should contact your GP for further review.

How can rectal bleeding be treated?

Treatment very much depends on the cause. Haemorrhoids can be treated by over-the-counter remedies. Constipation can be prevented by exercising regularly, drinking plenty of fluids and eating high fibre diets.

Cancer of the bowel requires specialist treatment and may need a combination of surgery, chemotherapy and radiotherapy to help manage the disease.

Inflammatory bowel disease requires medication and regular reviews by a specialist team.

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