Lower GI bleeding


Definition & classification

Lower gastrointestinal bleeding (LGIB) classically refers to bleeding that occurs distal to the ligament of Treitz.

The ligament of Treitz (suspensory ligament of the duodenum) marks the boundary between the upper and lower gastrointestinal (GI) tracts. It arises from the right crus of the diaphragm and suspends the duodenojejunal flexure.

Incidence of LGIB is 20 in 100,000 per population / year. Nevertheless, LGIB is thought to be an under-recognised condition because patients with minor LGIB may not seek medical attention. LGIB is more common with advancing age and in males.

Clinical presentation is variable; it is dependent on the underlying aetiology.

Aetiology & pathophysiology

There are numerous causes of LGIB, which can be grouped according to the gross underlying aetiology.

Causes of LGIB


  • Diverticular disease
  • Anorectal pathology (e.g. anal fissures, haemorrhoids)


  • Acute mesenteric ischaemia
  • Angiodysplasia


  • Polyps
  • Malignancy


  • Inflammatory bowel disease
  • Infective causes



Diverticulosis refers to the presence of multiple diverticuli within the bowel. It is the most common cause of LGIB, accounting for up to 40% of cases.

Diverticulosis is characterised by protrusions of the colonic mucosa through the muscularis externa. Technically these are false diverticuli as they do not involve the entirety of the bowel wall. Diverticulosis becomes more common with increasing age, occurring in 40-60% of patients over the age of 60. Approximately 75% of diverticuli occur within the sigmoid colon. 

Symptomatic bleeding is characteristically painless (or with mild symptoms). Up to 80% of cases will resolve spontaneously.

Diverticulosis may cause diverticular disease in the form of:

  • Diverticular bleeding - symptomatic diverticuli (e.g. painless bleeding).
  • Diverticulitis - inflammation of a diverticulum, multiple diverticuli or whole segments of bowel (typically due to infection). Diverticulitis can lead to the formation of abscesses and complications including fistulae and bowel perforations.


Anorectal pathology

Refers to a collection of conditions that affect the perianal area including: haemorrhoids, fissures, and anorectal fistulae.

Anorectal pathology is typically a cause of fresh rectal bleeding and more commonly presents in patients under 50 years old. It accounts for around 6-16% of LGIB. However, many cases of self-limiting bleeding may go unnoticed.

  • Haemorrhoids - dilatations in the anal cushions, which may engorge and prolapse through the anal canal. 
  • Fissures - tears in the anal mucosa, classically leading to exquisite pain on passing faeces (digital rectal examination may not be tolerated).
  • Fistulas - abnormal connections between two epithelial-lined surfaces. They cause a variety of symptoms and may be associated with anorectal abscesses.



Angiodysplasia refers to the presence of an arteriovenous malformation (AVM) located within the submucosa.

An AVM is an abnormal connection between an artery and vein. It can account for up to 3% of LGIB. It is the most common vascular cause of LGIB. Bleeding is usually less vigorous than other causes of LGIB, such as diverticular disease, although some patients may require interventional treatment to help locate and treat bleeding lesions.

Angiodysplasia is associated with a number of medical conditions; angiodysplasia in the presence of aortic stenosis is called Heyde’s syndrome.

Acute mesenteric ischaemia

A rare but significant cause of LGIB, associated with high morbidity and mortality.

Acute mesenteric ischaemia (otherwise known as ischaemic colitis) is caused by inadequate perfusion through the mesenteric vessels. It may be secondary to venous or arterial pathology.

Acute mesenteric ischaemia secondary to arterial pathology is usually divided into those caused by an in situ thrombus and those caused by an embolus (e.g. from left atrial appendage in patients with atrial fibrillation). The condition seldom causes significant blood loss. Instead, the characteristic findings are pain out of proportion to the findings on physical examination.


Neoplastic causes of LGIB can have a significant impact on morbidity and mortality.


Polyps are benign neoplastic proliferations of the colonic epithelium which possess small malignant potential. Multiple polyps may be seen in a number of familial conditions (e.g. familial adenomatous polyposis, hereditary non-polyposis colorectal carcinoma).


Colorectal carcinoma is a common, and significant, cause of LGIB that occurs more commonly in males. Accounts for 10% of cases of rectal bleeding in the over 50’s. Bleeding from a colorectal malignancy tends to be low grade but recurrent. Older patients presenting with LGIB should be investigated for potential underlying malignancy, and should be referred for urgent endoscopy within two weeks.


Inflammatory bowel disease

Inflammatory bowel disease is an umbrella term for ulcerative colitis & Crohn’s disease.

Ulcerative colitis (UC) and Crohn’s disease (CD) are chronic inflammatory disorders of the GI tract. Both conditions possess relapsing, remitting courses. They typically cause abdominal pain and LGIB.



These topics are covered in more detail in our notes on “ulcerative colitis” and “Crohn’s disease”.

Infective gastroenteritis

The presence of bloody diarrhoea may suggest a number of infective aetiologies which cause dysentery (low-volume, bloody diarrhoea with abdominal pain).

Infective causes of LGIB

A number of infective organisms may lead to bloody diarrhoea:

  • Escherichia coli
  • Shigella dysentery
  • Entamoeba histolytica
  • Campylobacter spp.

E. coli 0157 is an enterohaemorrhagic strain of E. coli which can lead to bloody diarrhoea. It may cause haemolytic uraemic syndrome (HUS), which classically presents as a triad of acute kidney injury (AKI), haemolytic anaemia and thrombocytopaenia.

There are three predominant mechanisms by which bacteria cause gastroenteritis:

  • Mucosal adherence - microorganisms attach to the GI mucosa via pili or fimbriae. These structures allow the bacterium to bind to epithelial cells and secrete effector molecules.
  • Mucosal invasion - invasion into the muscoa leads to damage to the epithelium through disruption of the cytoskeleton and cell-to-cell junctions. This mechanism classically causes the clinical picture of ‘dysentery’. 
  • Toxin production - the release of toxins can cause either direct damage to the epithelium and underlying structures (e.g. cytotoxins secreted by E. coli 0157) or may activate cellular mechanisms leading to excessive watery secretions (e.g. enterotoxins secreted by V. cholera).

Clinical features

The presentation of LGIB is classified according to the extent of bleeding.

A distinct set of clinical features can be seen in patients presenting with moderate bleeding, massive bleeding or occult bleeding.

Moderate bleeding

  • Pyrexia
  • Weight loss
  • Dizziness
  • Altered bowel habit
  • Abdominal pain
  • Haematochezia
  • Perianal disease
  • Melaena (consider UGI source)

Massive bleeding

  • Confusion
  • Dehydration
  • Tachycardic and hypotensive
  • Abdominal pain
  • Stigmata of chronic liver disease
  • Haematochezia

Clinical features of LGIB

Occult bleeding

The upper GI tract is 3-4 times more common as a source of bleeding and usually investigated first if patients present with unexplained iron-deficiency anaemia.

  • Fatigue
  • Dizziness
  • Pallor
  • Weight loss
  • Altered bowel habit
  • Vague abdominal pain

Investigations & diagnosis

The diagnosis of LGIB is a clinical diagnosis, and the requirement for further investigations is dependent on the suspected underlying aetiology.

In general, investigations help to determine the extent and location of bleeding. In some instances, they can offer haemostatic control (e.g. endoscopy). 

A full blood count (FBC) and digital rectal examination (DRE) are important initial tests for assessing LGIB. Depending on the presentation, some patients may then require imaging and/or endoscopic assessment.


  • Digital rectal examination
  • Observations
  • Lying / standing blood pressure
  • Blood glucose
  • ECG
  • Stool microscopy, culture & sensitivities
  • Faecal calprotectin


  • Full blood count (FBC)
  • Urea & electrolytes (U&Es)
  • Liver function tests (LFTs)
  • Haematinics
  • Clotting
  • Arterial / venous blood gas
  • Crossmatch (if bleeding is extensive)


  • Erect CXR (to rule out perforation)
  • Computed tomography (CT) and CT angiography


  • Flexible sigmoidoscopy
  • Colonoscopy
  • Upper GI endoscopy (e.g. if UGIB suspected)
  • Angiographic transarterial embolisation

A flexible sigmoidoscopy is useful in younger patients if there is any concern regarding the underlying pathology. A colonoscopy is considered the definitive test in patients where there is a high suspicion of malignancy.


The management of lower GI bleeding is largely dependent on the clinical presentation.

Patients presenting with an acute LGIB (e.g. moderate or massive bleeding) require initial assessment and resuscitation, followed by identification of the source of bleeding and haemostatic control.

Patients with occult bleeding may need an urgent referral for suspected gastrointestinal malignancy through the two-week wait cancer referral pathway.

Admission to hospital should be considered as part of the initial assessment.

Management of LGIB

Acute LGIB

Patients presenting with an acute LGIB (e.g. moderate or massive bleeding) require initial assessment and resuscitation followed by localisation +/- intervention.

Management of acute LGIB

1. Resuscitation

Resuscitation with respect to airway, breathing & circulation.

  • Airway
    • Patent and protected
  • Breathing
    • Saturations
    • Respiratory rate
  • Circulation
    • Blood pressure & heart rate
    • ECG
    • IV access & bloods
    • IV fluids (0.9% normal saline)
    • Blood products (RBC, FFP, platelets)

2. Localisation

Imaging and/or endoscopic investigations are carried out to help identify the source of bleeding.

Localisation of an acute LGIB is reliant on imaging or endoscopic investigations. Importantly, 10-15% of massive LGIBs occur from the upper GI tract. Haemodynamically stable patients with mild-to-moderate bleeding or stabilised massive bleeds should undergo colonoscopy.

3. Intervention

Once localised, the bleeding site can be coagulated via administration of vasoconstrictors or sclerosing agents. Angiography may be required to locate and control bleeding in patients where colonoscopy has been unsuccessful.

Occult LGIB

NICE recommends the referral of patients under the urgent cancer pathway who fulfil certain criteria.

Occult LGIB management

1. Urgent referral

Urgent two-week referral:

  • Age ≥ 40 with unexplained weight loss and abdominal pain.
  • Age ≥ 50 with unexplained rectal bleeding.
  • Age ≥ 60 with iron-deficiency anaemia (IDA) or change in bowel habit.
  • New rectal or abdominal mass
  • Unexplained IDA in men or post-menopausal women.

2. Identify pathology

Typically endoscopic investigation - upper GI endoscopy and colonoscopy with tissue biopsies. If no lesion is identified then consider further investigations such as computed tomography, small bowel imaging (e.g. capsule endoscopy), or angiography.

3. Management of anaemia

Iron-deficiency anaemia is managed with iron supplementation (e.g. ferrous sulfate 200mg TDS). Blood transfusions should only be used as a last resort in the non-acute setting.

Iron supplemetation should be held one week prior to endoscopic investigations, as it can impair the clarity of views.

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