Blood in stool: causes, red flags and when to seek help

Where the blood comes from tends to determine how it looks. Bright red blood on the toilet paper or dripping into the pan usually comes from low down, near the anus or rectum. Dark red blood mixed through the stool suggests a source higher in the large bowel. Black, tarry and strongly smelling stool, called melaena, suggests blood that has been digested on its way down from the stomach or upper gut.

Streaks on the surface of a hard stool suggest a tear in the skin of the anus. Blood mixed with mucus and diarrhoea can point towards inflammation of the bowel lining. Red food such as beetroot, and iron tablets, can mimic blood, so a close look and sometimes a test is needed to be sure.

The NHS describes piles (haemorrhoids) as lumps inside and around the bottom, listing bright red blood after you poo, an itchy anus, mucus on underwear or paper, lumps and pain around the anus among the symptoms. It says constipation, pushing too hard when pooing, heavy lifting, pregnancy, getting older and being overweight make piles more likely.

• Piles: bright red blood on the paper or in the pan, often without much pain.

• Anal fissure: a sharp, stinging pain when passing a hard stool, with a streak of fresh blood.

• Diverticular disease: sudden, sometimes heavy, painless bleeding in older adults.

• Inflammatory bowel disease: bloody diarrhoea, mucus, urgency and cramping.

• Infection: bloody diarrhoea with fever after contaminated food or travel.

• Polyps and bowel cancer: blood in the stool, often with a change in bowel habit, weight loss or tiredness.

• Bleeding higher up in the gut, from an ulcer or inflamed stomach, producing black stool.

The NHS lists the main symptoms of bowel cancer as including changes in your poo, such as softer poo, diarrhoea or constipation that is not usual for you, needing to poo more or less often, blood in the poo, feeling you need to poo even straight after going, tummy pain, a lump in the tummy, bloating, losing weight without trying and feeling very tired or short of breath, which can be signs of anaemia.

The NHS also stresses that these symptoms are very common and can have other causes, but it is important to be checked. A bleed that is combined with any of these, or that does not go away, deserves proper investigation even if piles seem the likely explanation.

For bleeding from the bottom, the NHS advises calling 999 or going to A&E if you are bleeding non-stop, if there is a lot of blood, or if you see large blood clots when you poo. Do not drive yourself; ask someone else or call an ambulance.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if your poo is black or dark red, if you have bloody diarrhoea, if you have piles with painless bleeding from the bottom, if pus leaks from piles, or if you feel hot, cold or shivery and generally unwell. Feeling faint, looking pale or being short of breath with bleeding suggests significant blood loss and is a reason for same-day assessment.

Vomiting blood, or vomit that looks like coffee grounds, together with black stools, is an emergency that needs A&E.

The NHS bowel cancer page says the doctor will ask about your symptoms, general health and medical history, and whether anyone in your family has had bowel cancer. Depending on your symptoms they may feel your tummy and ask to do a rectal examination, where a gloved finger is used to check for lumps. You can ask for a male or female clinician and for someone else to be present, and you will be asked to undress from the waist down for the examination.

Expect questions about the colour and amount of blood, whether it is on the paper, in the pan or through the stool, any pain, changes in bowel habit, weight change, medicines such as aspirin, anticoagulants or anti-inflammatories, and recent travel or contacts with diarrhoeal illness.

The NHS says you may be asked for a stool sample, or given a home kit called a faecal immunochemical test (FIT), which checks whether you are bleeding from your bowel. You may also have a blood test, which can show iron-deficiency anaemia. If the doctor thinks your symptoms could be cancer, an urgent referral may follow; the NHS says this does not definitely mean you have cancer.

• FIT test on a small stool sample.

• Blood tests including a full blood count and iron studies.

• Flexible sigmoidoscopy, which examines the lower bowel.

• Colonoscopy, which examines the entire large bowel and can remove polyps.

• CT colonography for some people who cannot have a colonoscopy.

If piles are the likely cause, the NHS suggests drinking lots of fluid, eating plenty of fibre, keeping the area clean and dry by patting rather than rubbing, and not pushing hard or spending a long time on the toilet. It advises against painkillers containing codeine because they can cause constipation, and against ibuprofen if your piles are bleeding. A pharmacist can suggest creams and laxatives.

Do not assume the cause is piles without a check if bleeding is persistent, if you are older, or if your bowel habits have changed. Try not to be embarrassed; clinicians discuss these symptoms every day.