There are many causes of rectal bleeding. The severity can vary from mild bleeding (common) to a severe life-threatening bleeding (uncommon). If the bleeding is heavy, or if you have melaena (black faeces due to a bleed from the stomach or duodenum) then see a doctor immediately or call an ambulance. However, it is often a mild bleed. In this situation, make an appointment with your doctor so that the cause can be found.
What is rectal bleeding?
The term rectal bleeding is often used by doctors to mean any blood that is passed out when you go to the toilet to pass faeces. However, not all bleeding that is passed out actually comes from the rectum. The blood can come from anywhere in the gut (the gastrointestinal tract). The more correct term is gastrointestinal tract bleeding, often abbreviated to GI bleeding. There are many causes of rectal bleeding (GI bleeding) which are discussed later.
What is the gut?
The gut (gastrointestinal tract) starts at the mouth and ends at the anus. When we eat or drink, the food and liquid travel down the oesophagus (gullet) into the stomach. The stomach churns up the food and then passes it into the small intestine.
The small intestine (sometimes called the small bowel) is several metres long and is where food is digested and absorbed. Undigested food, water and waste products are then passed into the large intestine (sometimes called the large bowel). The main part of the large intestine is called the colon, which is about 150 cm long. This is split into four sections: the ascending, transverse, descending and sigmoid colon. Some water and salts are absorbed into the body from the colon. The colon leads into the rectum (back passage) which is about 15 cm long. The rectum stores faeces (stools) before they are passed out from the anus.
Types of rectal bleeding / GI tract bleeding
When you have GI bleeding, the things that a doctor needs to asses include the following:
Severity of the bleeding
Bleeding can range from a mild trickle to a massive life-threatening severe bleed (a severe haemorrhage). In many cases the bleed is mild and intermittent. In this situation, any tests that need to be done, can be done as an outpatient. There is no immediate risk to life with mild, intermittent GI bleeding. However, always report to a doctor if you have a large amount of bleeding, as a lot of blood loss needs urgent treatment.
Sometimes bleeding from a condition in the gut is so mild (like a slight trickle) that you do not notice any actual bleeding and it is not enough to change the colour of your faeces. However, a test of your faeces can detect even small amounts of blood. This test may be done in various situations (described later).
Site of the bleeding
Bleeding can come from anywhere in the GI tract. As a general rule:
- Bleeding from the anus or low down in the rectum - the blood tends to be bright red and fresh. It may not be mixed in with faeces but instead you may notice blood after passing faeces, or streaks of blood covering faeces. For example, bleeding from an anal fissure or from haemorrhoids (described later).
- Bleeding from the colon - often the blood is mixed up with faeces (motions or stools). The blood may be a darker red. For example, bleeding from colitis, diverticula disease, or from a bowel tumour. However, sometimes, if the bleeding is brisk, then you may still get bright red blood not mixed up too much with faeces. For example, if you have a sudden large bleed from a diverticulum (described later).
- Bleeding from the stomach or small intestine - the blood has far to travel along the gut before it is passed out. During the time it takes to do this the blood becomes altered and dark and mixes with faeces. This can make your faeces turn a black or plum colour - this is called melaena. For example, this may occur due to a bleeding stomach or duodenal ulcer. Note: if you have melaena it is a medical emergency, as it usually indicates a lot of bleeding that is coming from the stomach or duodenum. You should tell a doctor immediately if you suspect that you have melaena.
The cause of the bleeding
A doctor may ask various questions to get an idea as to the main possible causes of the bleeding. So, for example, you may be asked about possible symptoms such as pain and, if you have any pain, the site and nature of the pain. Also if you have diarrhoea, weight loss, or other relevant symptoms. The doctor is then likely to examine you. This may include examining your back passage (anus and rectum) by inserting a gloved finger into your anus. Sometimes, a diagnosis can be made after this. For example, of an anal fissure or haemorrhoid. However, tests are commonly needed to clarify the cause.
What are the causes of rectal bleeding / GI tract bleeding?
There are many possible causes. Below is a brief overview of the more common causes:
Haemorrhoids are swellings that can occur in the anus and lower rectum. There is a network of small veins (blood vessels) within the inside lining of the anus and lower rectum. These veins sometimes become wider and engorged with more blood than usual. These engorged veins and the overlying tissue may then form into one or more small swellings called haemorrhoids. About half the people in the UK develop one or more haemorrhoids at some stage. Small haemorrhoids are usually painless. The most common symptom is bleeding after going to the toilet. Larger haemorrhoids may cause a mucous discharge, some pain, irritation, and itch. See separate leaflet called Haemorrhoids (Piles) for details.
An anal fissure is a small tear of the skin of the anus. Although the tear of an anal fissure is usually small (usually less than a centimetre), it can be very painful because the anus is very sensitive. Often an anal fissure will bleed a little. You may notice blood after you pass faeces. The blood is usually bright red and stains the toilet tissue, but soon stops. See separate leaflet called Anal Fissure for details.
A diverticulum is a small pouch with a narrow neck that sticks out from the wall of the gut. Diverticula means more than one diverticulum. They can develop on any part of the gut (intestines), but usually occur in the colon. Several diverticula may develop over time. A diverticulum may occasionally bleed and you may pass some blood via your anus. The bleeding is usually abrupt and painless. The bleeding is due to a burst blood vessel that sometimes occurs in the wall of a diverticulum and so the amount of blood loss can be heavy. See separate leaflet called Diverticula for details.
Crohn's disease is a condition which causes inflammation in the gut. The disease flares up from time to time. Symptoms vary, depending on the part of the gut affected and the severity of the condition. Common symptoms include bloody diarrhoea, abdominal pain, and feeling unwell. See separate leaflet called Crohn's Disease for details.
Ulcerative colitis and other forms of colitis
Ulcerative colitis (UC) is a disease where inflammation develops in the colon and rectum. A common symptom when the disease flares up is diarrhoea mixed with blood. The blood comes from ulcers that develop on the inner wall of the inflamed gut. There are other rare causes of colitis (inflammation of the colon) or proctitis (inflammation of the rectum) that can cause rectal bleeding. See leaflet called Ulcerative Colitis for details.
A bowel polyp (adenoma) is a small growth that sometimes forms on the inside lining of the colon or rectum. Most develop in older people. About 1 in 4 people over the age of 50 develop at least one bowel polyp. Polyps are benign (non-cancerous) and usually cause no problems. However, sometimes a polyp bleeds and sometimes a polyp can turn cancerous. See separate leaflet called Colonic (Bowel) Polyps for details.
Cancer of the colon and rectum are common cancers in older people. They sometimes affect younger people. Rectal bleeding is one symptom that may occur. Bleeding is often occult (not obvious - see later) and other symptoms are often present before visible bleeding occurs. For example, pains, anaemia, weight loss, diarrhoea or constipation. Cancers of other parts of the gut higher up from the colon sometimes cause rectal bleeding, but these are uncommon. See separate leaflet called Colorectal (bowel) cancer for details.
Angiodysplasia is a condition where you develop a number of enlarged blood vessels within the inner lining of the colon. Angiodysplasia most commonly develops in the ascending (right) colon, but they can develop anywhere in the colon. The cause is unknown, but they occur most commonly in older people. Bleeding from an angiodysplasia is painless. The blood seen can range from bright red brisk bleeding, to dark blood mixed with faeces, to melaena. An angiodysplasia may also cause occult blood loss (see below).
Abnormalities of the gut
Various abnormalities of the gut, or the gut wall may cause rectal bleeding in young children. For example: volvulus, intussusception, Meckel's diverticulum, abnormal blood vessel development.
Stomach and duodenal ulcers
Some gut infections
May cause bloody diarrhoea due to inflammation of the gut, caused by some infections.
There are various other rarer causes.
What should I do if I have rectal bleeding?
See a doctor. If the bleeding is heavy, or if you have melaena (described above), see a doctor immediately or call an ambulance. If you feel dizzy, collapse or feel generally unwell then consider calling an ambulance, as this might indicate a heavy bleed. However, often the bleeding is mild. In this situation, make an appointment with your doctor soon. Some people assume that their rectal bleeding is due to haemorrhoids (piles) and do not get it checked out. Haemorrhoids are perhaps the most common cause of rectal bleeding. However, you should not assume the bleeding is coming from a haemorrhoid unless you have been properly assessed by a doctor.
What tests might be advised?
It depends on the possible causes of the bleeding, which may be determined by a doctor talking to you (your history) and an examination. Two of the most common tests done when someone has rectal bleeding are called colonoscopy and sigmoidoscopy.
What is a colonoscopy?
A colonoscopy is a test where an operator (a doctor or nurse) looks into your colon.
A colonoscope is a thin, flexible telescope. It is about as thick as a little finger. It is passed through the anus and into the colon. It can be pushed all the way round the colon as far as the caecum (where the small and large intestine meet).
The colonoscope contains fibre optic channels which allow light to shine down so the operator can see inside your colon. This is done either by looking down the colonoscope, or by attaching the colonoscope to a TV monitor.
The colonoscope also has a side channel down which devices can pass. These can be manipulated by the operator. For example, the operator may take a small sample (biopsy) from the inside lining of the colon by using a thin grabbing instrument which is passed down a side channel. See separate leaflet called Colonoscopy for details.
What is a sigmoidoscopy?
The sigmoid colon is the final portion of the bowel that is joined to the rectum. A sigmoidoscope is like a small telescope with an attached light source about the thickness of your finger. It is similar to a colonoscope but much shorter. A sigmoidoscopy is easier to do than a colonoscopy. It may be done instead of a colonoscopy if the bleeding is suspected to be coming from the lower colon or rectum. A doctor or nurse inserts the sigmoidoscope into the anus and pushes it slowly into the rectum and sigmoid colon. This allows the doctor or nurse to see the lining of the rectum and sigmoid colon. The procedure is not usually painful but it may be a little uncomfortable. See separate leaflet called Sigmoidoscopy for details.
What is a faecal occult blood test?
The faecal occult blood test (FOB test) detects small amounts of blood in your faeces which you would not normally see or be aware of.
When and why is the faecal occult blood test done?
As discussed, there are several disorders which may cause bleeding into the gut. These may cause rectal bleeding which you can see. However, some of these disorders in some people may only bleed with a trickle of blood. If you only have a small amount of blood in your faeces then the faeces look normal. However, the FOB test will detect the blood. So, the test may be done if you have other symptoms that may suggest a gut problem. For example, persistent abdominal (tummy) pain, weight loss, etc. It may also be done to screen for bowel cancer before any symptoms develop (see below).
Note: the FOB test can only say that you are bleeding from somewhere in the gut. It cannot tell from which part. If the test is positive then further tests will usually be arranged to find the source of the bleeding. For example, colonoscopy.
How is the faecal occult blood test done?
A small sample of faeces is smeared on to a piece of card. You obtain a sample by using a small scraper to scrape some faeces off toilet tissue which you have just used after going to the toilet. The sample is tested by adding a chemical to the sample on the card. If there is a change in colour after adding the chemical, it indicates that some blood is present.
A doctor may do this test in the GP surgery, or send a sample to the laboratory for testing. Also, if required, there are test kits that you can get at pharmacies which enable you to do the test at home. Some people are issued with test kits to do testing at home.
Sometimes two or three FOB tests are done on two or three separate samples of faeces, obtained on different days. This is because a bleeding disorder of the gut may only bleed now and then. So, not every sample may contain blood. A series of two or three samples done on several days may be more accurate in detecting a bleeding gut disorder.
See separate leaflet called Faecal Occult Blood test for more details.
Screening for bowel cancer
Screening means looking for early signs of a particular disease in otherwise healthy people who do not have any symptoms and when treatment is likely to be curative. Colorectal cancer (bowel cancer) screening aims to detect colorectal cancer at an early stage when there is a good chance that treatment will cure the cancer.
As colorectal cancer is much more common in older people, the decision has been made for people of a certain age to be invited to participate in the colorectal cancer screening programme. This involves testing three samples of your faeces (stools or motions) for blood. The NHS Bowel Cancer Screening Programme has been introduced in the UK as follows:
- In England, people aged 60 to 69 will be routinely offered screening every two years. If you are aged 70 or over and screening has started in your area, you can phone the helpline on 0800 707 60 60 to request the kit, if you would like to have screening. From 2014, screening will be extended to cover people up to age 74 as standard.
- In Scotland, people aged 50 to 74 will be offered screening every two years.
- In Wales, people aged between 60-74 years who live in Wales will be asked to take part.
- In Northern Ireland, people aged between 60-71 will be offered screening every two years.
If you are in the relevant age groups, you will automatically be sent an invitation, and then your faecal occult blood (FOB) screening kit, so you can do the test at home. After your first screening test, you will then be sent another invitation and screening kit every two years until you reach the maximum age. You can then request further kits if you would like to continue to be included in the screening programme.
For more details see separate leaflet called Screening for Colorectal (Bowel) Cancer.
What is the treatment for rectal bleeding?
The treatment depends on the cause. See individual leaflets on the various diseases that can cause rectal bleeding.
Further help and information
The NHS Bowel Cancer Screening Programme
England - Helpline: 0800 707 6060
Scotland - Helpline: 0800 012 1833
Wales - Helpline: 0800 294 3370
Northern Ireland - Helpline: 0800 015 2514
Further reading & references
- Rana A, Lower Gastrointestinal Bleeding Imaging, Medscape, May 2011
- Choi HK, Law WL, Chu KW; The value of flexible sigmoidoscopy for patients with bright red rectal bleeding. Hong Kong Med J. 2003 Jun;9(3):171-4.
- Lohsiriwat V; Hemorrhoids: From basic pathophysiology to clinical management. World J Gastroenterol. 2012 May 7;18(17):2009-17.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Tim Kenny
Dr Hayley Willacy
Dr John Cox