Rectal Bleeding: What Does Blood from the Back Passage Mean?

Rectal bleeding is blood coming from the back passage, during a bowel movement or apart from one. It may be no more than a few drops on the toilet paper, or it may be on the surface of the stool, in the pan, or mixed through the stool.

Rectal bleeding is not a disease but a finding.

Its commonest causes are benign conditions such as haemorrhoids and anal fissure. But polyps, colitis and colorectal cancer can also bleed, so repeated bleeding should not simply be put down to haemorrhoids.

What does the appearance of the blood tell us?

• Bright red blood Usually seen when the bleeding comes from the anus, the rectum or the lower part of the large bowel. Haemorrhoids and anal fissure are common causes.
• Blood mixed through the stool If the blood is mixed into the stool, the bleeding may come from higher up in the colon. Polyps, colitis, diverticular disease or tumours may need to be considered.
• Black, tarry stool This is called melaena, and it usually suggests bleeding from the upper digestive tract, such as the stomach or duodenum.

But it is not possible to locate the bleeding with certainty from the colour of the blood alone.

What are the common causes of rectal bleeding?

Haemorrhoids — Bright red blood, usually during or after a bowel movement. Most often painless.

Anal fissure — Bright red blood, particularly after passing a hard stool, together with severe anal pain and burning.

Diverticular bleeding — Can cause painless bleeding that starts suddenly and may be heavy.

Colitis — In ulcerative colitis, Crohn’s disease, and infectious or ischaemic colitis, the bleeding may come with diarrhoea, mucus, abdominal pain and urgency.

Colon polyps — Most polyps do not bleed, but some can cause occult or visible bleeding.

Colorectal cancer — Rectal bleeding may occur together with a change in bowel habit, iron deficiency anaemia or weight loss.

Angiodysplasia — Particularly in later life, can cause repeated bleeding from the blood vessels in the bowel wall.

Can one say “I have haemorrhoids, so that is where the blood is from”?

Not always.

Haemorrhoids bleed very often; but the presence of haemorrhoids does not show that there is no other cause of bleeding.

Particularly with new or repeated bleeding, the patient’s age, family history, the character of the bleeding and any accompanying symptoms must all be assessed.

When is a colonoscopy needed?

A colonoscopy is not automatically needed for every few drops of rectal bleeding. But it may be needed where there is;

• Repeated or unexplained bleeding
• A new change in bowel habit
• Iron deficiency or anaemia
• Unexplained weight loss
• A family history of colorectal cancer or advanced polyps
• New bleeding in later life
• A suspicion of inflammatory bowel disease

Examination of the anal region and a rectal examination are important too.

Does rectal bleeding mean cancer?

No. In most cases the cause of rectal bleeding is not cancer.

But “the blood is bright red, so it must be haemorrhoids” is not right either.

Colorectal cancer can present with rectal bleeding before it causes any other symptom. That is why the cause of new or repeated bleeding should be established.

When is urgent assessment needed?

In short

• Rectal bleeding Is a finding; its cause should be sought.
• The commonest causes Are haemorrhoids and anal fissure.
• Rectal bleeding Does not by itself mean cancer.
• Having haemorrhoids Does not prove the blood is coming from them.
• Repeated or unexplained bleeding Should be assessed by a doctor.
• Heavy bleeding with dizziness or fainting Needs urgent assessment.