Private blood in the stool clinic in London, same-day gastroenterology.

What the appearance suggests

• Bright red on the paper or dripping into the pan, not mixed with the stool — usually haemorrhoids or an anal fissure.
• Bright red mixed through the stool — from higher in the large bowel; needs investigating.
• Dark red or maroon, mixed in — from further up the bowel.
• Black and tarry (melaena), with a distinctive smell — from the stomach or small bowel. An emergency.
• Mucus with blood — suggests inflammation, polyps or infection.
• Pain on passing stool with bright blood — typically a fissure, which is intensely painful and benign.

Features that need urgent investigation

• bleeding with a persistent change in bowel habit lasting three weeks or more
• unexplained weight loss, or a lump in the abdomen
• iron deficiency anaemia
• bleeding over the age of 50, particularly if new
• a family history of bowel cancer, especially under 50
• bleeding that persists despite treatment for piles or a fissure

The FIT test

The faecal immunochemical test detects tiny amounts of blood invisible to the eye. It is used both in national bowel screening and, increasingly, to assess symptoms — a negative FIT substantially reduces the likelihood of significant bowel disease and can avoid an unnecessary colonoscopy, while a positive result prompts one. It is a single small sample done at home.

What investigation involves

• Examination, including a rectal examination and often proctoscopy — brief, undignified, and it finds most causes
• Blood tests — full blood count and ferritin, to detect anaemia and iron loss
• FIT test
• Stool tests for infection and calprotectin where inflammation is suspected
• Colonoscopy — the definitive test, allowing polyps to be removed at the same time
• CT colonography as an alternative where colonoscopy is unsuitable

Treating the common causes

• Haemorrhoids — increase fibre and fluid, avoid straining and prolonged sitting on the toilet, topical treatment for symptoms, and banding or surgery if persistent.
• Anal fissure — the pain causes spasm which prevents healing, so treatment aims to relax the muscle: stool softeners, and a prescribed ointment such as GTN or diltiazem for six to eight weeks.
• Treat constipation properly in both, because straining is what caused and sustains them.