What should you know about blood in stool, vomiting and diarrhoea?

Gastroenteritis can cause vomiting and diarrhoea, sometimes with blood, while Crohn's Disease and Ulcerative Colitis can inflame the bowel and cause bloody diarrhoea. Diverticular Disease and other bowel problems may also bleed. Black tar-like stool points to digested blood rather than fresh bleeding near the anus. The combination can make dehydration develop quickly, so clinicians need the full history instead of relying on one symptom.

Contact a clinician promptly. Take frequent small sips of water or an oral rehydration drink if you can keep fluids down; pause briefly after vomiting and try again. Avoid alcohol, greasy meals, and anti-diarrhoeal medicines unless advised when stool contains blood. Wash hands carefully and avoid preparing food for others until an infectious cause is considered. Record stool and vomit appearance, fever, pain, travel, and recent food exposures.

Seek emergency help for fainting, confusion, severe weakness, very little urine, a dry mouth with inability to drink, severe abdominal pain, repeated vomiting, heavy bleeding, or black tarry stool. A child, older adult, pregnant person, or someone with a serious long-term condition may need urgent advice sooner because fluid loss can be harder to manage.

Could this be an infection or bowel inflammation? How can I replace fluids safely? Do I need stool or blood tests? Which changes mean I should go straight to emergency care?