When to worry about blood in stool if you have rectal cancer

Bleeding may come from the tumour, irritation in the rectum, haemorrhoids, a small tear, infection, or treatment effects. Bright red blood often comes from the lower bowel, while dark or tarry stool can indicate bleeding higher in the digestive tract. The appearance alone cannot identify the cause.

Record when the bleeding appears, its colour, whether it coats the stool or is mixed through it, and whether you have pain, mucus, diarrhoea, constipation, or urgency. Continue prescribed medicines unless your clinician tells you otherwise. Arrange a review with your oncology or colorectal team, even if bleeding settles.

Seek emergency help for heavy or continuous bleeding, black tarry stools, fainting, confusion, marked weakness, a racing heartbeat, severe abdominal pain, fever, or inability to pass stool or gas. These signs can indicate significant bleeding, infection, or bowel obstruction and need immediate assessment.

Ask whether the bleeding could relate to the tumour, treatment, or another bowel problem; which symptoms should trigger emergency care; whether medicines need review; and which tests or examination are appropriate.