Seeing blood in your stool or on toilet paper does not always mean cancer. Haemorrhoids and anal fissures are possible causes, but they cannot be reliably distinguished by appearance alone, so new, recurrent or unexplained bleeding should be assessed by a doctor. A previous diagnosis of haemorrhoids does not prove that every new episode of bleeding is due to them.
Emergency care is needed if bleeding is heavy or does not stop, there are large clots, or you develop dizziness, fainting, cold sweats or shortness of breath. Black, tar-like stools, dark red blood and bloody diarrhoea also require urgent medical assessment on the same day. Do not drive yourself if you feel weak or have signs of blood loss.
What can the colour of the blood indicate?
Bright red blood often comes from the anus, rectum or lower colon. A mark on the paper, a streak on the stool or drops in the toilet may be consistent with haemorrhoids or a fissure, but other conditions can cause the same pattern of bleeding. There may be no pain.
Dark red blood mixed with stool can occur with bleeding from higher up the bowel. Black, sticky, tar-like stools often suggest bleeding from the stomach or upper digestive tract. Blood darkens as it changes during its passage through the digestive tract, but the rate of bleeding and transit time also affect its appearance, so colour alone cannot pinpoint the source.
Iron supplements and some foods can darken stool, while foods such as beetroot can turn it red. Before attributing a colour change to medication or food, consider how you feel and the nature of the change. If you have tar-like stools, weakness or dizziness, taking iron supplements is not a reason to delay assessment.
Blood may not be visible. Small amounts of blood loss that cannot be seen with the naked eye can deplete iron stores and cause anaemia if they continue over time. Anaemia is a reduction in haemoglobin, which carries oxygen in the blood; it may cause tiredness, pallor and becoming short of breath easily during physical activity.
How do the possible causes differ?
Haemorrhoids are enlarged vascular cushions in the anal canal that cause symptoms. Internal haemorrhoids often cause painless, bright red bleeding; itching and a swelling that protrudes outside the anus may also occur. An anal fissure is a small tear in the lining of the anus. Sharp pain and a small amount of bright red blood, particularly after passing a hard stool, may be consistent with a fissure.
Some polyps, tissue growths on the inner lining of the bowel, can bleed, but most cause no symptoms and are found incidentally during an examination for another reason. Colon and rectal cancer are also possible causes of bleeding. This possibility is investigated more closely when blood is accompanied by a persistent change in bowel habits, unexplained weight loss or anaemia.
Ulcerative colitis and Crohn's disease are long-term inflammatory bowel diseases. They can cause bloody diarrhoea, abdominal cramps, mucus and an urgent need to go to the toilet. Because infections can cause similar symptoms, the doctor considers factors such as how long symptoms have lasted, fever, recent travel and antibiotic use to distinguish between the causes.
Bleeding can also come from diverticula, small pouches in the bowel wall, and fragile blood vessels. Sometimes this bleeding is heavy but painless. Assuming that it cannot be serious because there is no pain is therefore not a safe way to judge it.
Medicines that reduce blood clotting can make existing bleeding worse. Aspirin and some painkillers may also be associated with damage to the digestive tract and bleeding. However, taking medication does not remove the need to look for an underlying cause. Any decision to stop a regular medicine or change its dose should be made with a doctor.
What information is needed at the appointment?
You will be asked when you first noticed blood, how long it has been present, whether it happens every time and whether it is mixed with the stool. Describing the colour is helpful, but you are not expected to measure the amount precisely or make a diagnosis. Information about pain, diarrhoea, constipation, weight loss and a family history of bowel cancer helps guide the choice of investigations.
The doctor assesses your general condition, pulse and blood pressure. They may examine the abdomen and anal area and, if needed, examine the rectum with a gloved finger. Looking inside the anal canal with a short instrument is called anoscopy and helps identify local causes such as haemorrhoids.
You can mention any anxiety or reluctance about the examination during the appointment. The procedure will be explained beforehand. Even if a local cause is found, investigations may not end there if additional risks or warning signs are present. Having haemorrhoids does not guarantee that there is no problem elsewhere in the bowel.
Which tests and examinations are used?
A full blood count provides information about anaemia. Ferritin, which reflects iron stores, and other blood tests may be requested to assess the effects of long-term blood loss. Heavy bleeding requires clotting tests and additional urgent blood tests. For bloody diarrhoea, stool tests for infection and inflammation may be chosen.
Colonoscopy uses a flexible instrument with a camera to show the inner lining of the colon and rectum. A small tissue sample can be taken from a suspicious area during the examination; this is called a biopsy. For some people, an examination of only the lower bowel may be sufficient, while a full colonoscopy is more appropriate for others. The choice depends on age, symptoms, family history and the initial examination.
If bleeding from the stomach or upper digestive tract is suspected, gastroscopy, an examination using a camera-equipped instrument passed through the mouth, may be needed. For ongoing heavy bleeding, a CT scan using a special substance injected into a vein may be chosen in hospital. This imaging helps locate the source of bleeding. Not everyone needs all these tests.
If bleeding recurs after stopping, keep your scheduled appointment. However, new heavy bleeding, fainting or severe abdominal pain changes the previous plan and requires emergency care. Including the time of the last dose as well as the name of each medicine on the list you give the doctor helps with assessing the bleeding and planning subsequent treatment.