When to worry about blood in stool with bowel cancer

Bowel cancer can bleed from a growth in the colon or rectum. Blood may be bright red, darker, or mixed into the stool. A change in bowel habit, narrower stools, abdominal discomfort, tiredness, or unplanned weight loss can occur too, although symptoms vary.

Bleeding alone cannot show whether bowel cancer is stable, progressing, or caused by another problem. Your clinician may need to review your symptoms, examination findings, blood tests, and bowel investigations together.

Tell your cancer team or doctor about any fresh bleeding, a change in its pattern, or blood that returns after treatment. Mention constipation, diarrhoea, pain, dizziness, and medicines such as anticoagulants. Keep taking prescribed treatment unless your clinician tells you otherwise.

Note the colour and amount of blood, when it appears, and whether it is on the paper, coating the stool, or mixed through it. This information helps the team decide how quickly you need assessment.

Go to urgent care for heavy or continuous bleeding, black tar-like stool, fainting, confusion, severe abdominal pain, a swollen abdomen, repeated vomiting, or inability to pass stool and gas. Seek prompt help for breathlessness, paleness, or sudden marked weakness.

Ask what bleeding should trigger an immediate call, whether your medicines affect bleeding, and which tests may clarify the cause. Ask who to contact overnight and how to manage constipation or diarrhoea safely.