Bloody diarrhoea causes: what to know

Food Poisoning and Gastroenteritis can begin suddenly with cramps, fever, nausea or vomiting. Giardiasis may follow contaminated water or food and can cause prolonged loose stools. Crohn's Disease can cause recurring bowel inflammation, while Coeliac Disease is linked to an immune reaction to gluten and may affect digestion. Food Intolerance and Hyperthyroidism can change bowel habits, but visible blood needs its own explanation. Irritable Bowel Syndrome may cause pain and altered stools without bleeding. The presence of diarrhoea does not tell you which condition you have.

Write down the onset, stool frequency, blood colour, pain, fever, weight change and recent travel or antibiotic use. Maintain fluids with water or an oral rehydration drink. Seek an appointment for new, persistent or recurrent bleeding; testing may be chosen according to the pattern and examination. Do not remove major food groups for a long period without advice.

Get urgent medical help for increasing blood loss, black stools, severe abdominal pain, faintness, confusion, repeated vomiting, high fever or very little urine. A rapid change in symptoms or marked weakness should not wait for a routine appointment.

Ask which cause best fits the timing and associated symptoms, whether stool or blood tests are appropriate, and what you should eat and drink during assessment. Mention family bowel history and every regular medicine.