What causes rectal bleeding and when to seek help

Rectal bleeding refers to passing blood through your back passage (rectum). Depending on the underlying cause of your rectal bleeding, the blood can vary in colour.

Bright red blood usually suggests bleeding from your anus, rectum or lower colon. Darker, maroon blood usually refers to bleeding higher up in your colon, while black or tarry blood usually refers to bleeding in your upper gastrointestinal tract (ie your gullet, stomach and the first part of your small intestine).

Common causes of rectal bleeding

If you’re passing bright red blood, one of the most common causes is haemorrhoids, more commonly known as piles. Piles are swollen lumps in and around your anus and are often caused by straining too much when opening your bowels, such as when you’re constipated. Passing bright red blood can also be caused by an anal fissure, which is a tear in your anus. 

If you are passing intermittent darker blood, which suggests bleeding further up in your colon, this may be a consequence of diverticulosis, where small pouches develop in the lining of your colon, usually with age. If these pouches become infected or inflamed, nearby small blood vessels can bleed. 

In older patients, rectal bleeding may be a sign of bowel cancer.

Other common causes of rectal bleeding include anal fistulas, inflammatory bowel disease (Crohn’s disease or ulcerative colitis), a stomach ulcer, bowel polyps or as a side effect of blood-thinning medication. 

When to see your GP

If you have a history of piles, can feel a lump in or around your anus and your symptoms, including rectal bleeding, aren’t having a significant impact on your quality of life, you may feel comfortable managing your condition at home.

However, in general, if you develop any new rectal bleeding, you should always see your GP within one to two weeks to identify the cause and rule out bowel cancer.

When to seek urgent medical attention

If you’re bleeding heavily (eg filling the toilet pan) and/or feel unwell as a result of your rectal bleeding, go to your nearest A&E. Although rectal bleeding is rarely fatal, it’s important to address the underlying cause.

Investigating rectal bleeding

If you have rectal bleeding, your doctor will ask you about your medical history and your symptoms, specifically when your symptoms started, when bleeding occurs and the colour of the blood.

You may need a physical examination and/or a colonoscopy, where a thin, telescope-like tube with a light and camera on the end is passed into your rectum. This will allow your doctor to examine your colon and look for the source of the bleeding. If only the first third of your colon needs to be examined, you may have a sigmoidoscopy, where the telescope-like tube is not passed as far up into your colon.

Before having a colonoscopy or sigmoidoscopy, your doctor will advise you on how to prepare for the investigation, which will include taking a bowel preparation to clear out your bowels.

Once the cause of your rectal bleeding has been identified, your doctor will explain the best course of treatment to stop your bleeding and reduce the risk of it returning.