Part of the TeachMe Series

Rectal Bleeding

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Original Author(s): Ryan Cohen
Last updated: March 25, 2019
Revisions: 8

Original Author(s): Ryan Cohen
Last updated: March 25, 2019
Revisions: 8

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Rectal bleeding (or haematochezia) is the passage of fresh blood per rectum. It is generally caused by bleeding from the lower gastrointestinal tract, but may occur in patients with large upper GI bleeds or from small bowel lesions.

The causes of rectal bleeding range from benign to life-threatening disease and can result in significant haemodynamic instability if not managed appropriately.

In this article, we shall look at the causes, key clinical features, investigations, and management of haematochezia.

Figure 1 – The blood supply of the large bowel

Differential Diagnosis

Fresh rectal bleeding most commonly results from a source in the rectum or colon, however large upper GI bleeds can present as haematochezia (a patient with a large fresh rectal bleed who is haemodynamically unstable has an upper GI bleed until proven otherwise).

Causes of acute lower GI bleeding include diverticulosis, ischaemic or infective colitis, haemorrhoids, malignancy, angiodysplasia, inflammatory bowel disease, or radiation procititis.


Diverticulosis is the most common cause of lower gastrointestinal bleeding. Diverticula are outpouchings of the bowel wall that are composed only of mucosa, most commonly in the descending and sigmoid colon.

Their incidence increases with age. Diverticular disease bleeds are classically painless, whilst diverticulitis is classically painful.


Figure 2  – Haemorrhoids located in the 3, 7, and 11 o’clock positions

Haemorrhoids are pathologically engorged vascular cushions in the anal canal that can present as a mass, with pruritus, or fresh red rectal bleeding.

The blood is classically on the surface of the stool or toilet pan, rather than mixed in with it. Large haemorrhoids can also thrombose which can be extremely painful.


With any case of PR bleeding, especially in the elderly population, malignancy should be suspected, as this may be a colorectal cancer.

In the assessment of any patient with haematochezia, it is important to enquire about other lower GI symptoms, weight loss, or relevant family history, potentially suggestive a diagnosis of malignancy.

Clinical Features

Key aspects to ascertain from clinical assessment include:

  • Nature of bleeding, including duration, frequency, colour of the bleeding, relation to stool and defecation
  • Associated symptoms, including pain (especially association with defaecation), haematemesis, PR mucus, or previous episodes
  • Family history of bowel cancer or inflammatory bowel disease

A PR examination is essential for every patient presenting with haemotochezia, allowing assessment for any rectal masses or anal fissures


All patients presenting with rectal bleeding should have routine bloods* (FBC, U&Es, LFT, coagulation studies) and a Group and Save requested (as a minimum).

The presence of an elevated serum urea to creatinine ratio (>30:1) suggests an upper GI source of bleeding being more likely. Stool cultures are also useful to exclude infective causes.

*Acute bleeds may not initially show reduced Hb level due to haemoconcentration, however ongoing bleeding will show a reduced Hb 

Endoscopy and Imaging

Patients who are haemodynamically stable require a flexible sigmoidoscopy for further assessment, importantly to exclude left-colonic pathology (especially malignancy) and can often be performed as an outpatient. If flexible sigmoidoscopy proves inconclusive, patients may undergo a full colonoscopy (especially if symptoms suggest more proximal disease).

In patients who are haemodynamically unstable, an emergency upper GI endoscopy must also be considered in such patients and can be performed immediately before colonoscopy, alongside ongoing resuscitation.

CT angiography (or radionuclide labelled red-cell scintigraphy) can be used in patients with colonoscopy was non-diagnostic, endoscopic haemostasis unsuccessful, or with ongoing bleeding and haemdynamic instability. Not only can this aid in the identification of culprit bleeding vessels but also permits for potential therapeutic intervention if possible, via arterial embolisation.

Figure 3 – Endoscopic image of angiodysplasia being treated with argon plasma coagulation

Risk factors for adverse outcomes from any acute rectal bleeding (i.e. recurrent bleeding, need for intervention, or death) include haemodynamic instability, ongoing haematochezia, age >60yrs , serum creatinine >150µmol/L, or significant co-morbidities.


Any acute large rectal bleed warrants careful resuscitation, with a standard A to E approach, gaining 2 large bore cannulae, IV fluid, and blood products crossmatches (as required).

95% of cases will settle spontaneously. Patients who are stable and are otherwise fit, in whom the bleeding has stopped and who have a normal Hb, can often be discharged, to be investigated as an outpatient; older or co-morbid patients may need admission for observation regardless.

A minority of patients become haemodynamically unstable or have ongoing bleeding:

  • For those who undergo endoscopy, endoscopic haemostasis methods include injection (typically diluted adrenaline), contact and non-contact thermal devices (such as bipolar electrocoagulation or argon plasma coagulation), and mechanical therapies (endoscopic clips and band ligation)
  • For those who undergo angiography, arterial embolisation can be trialled, especially if the vessel is identifiable and sufficient diameter

Surgical Intervention

Surgical intervention may be required in patients with ongoing lower GI bleeding with instability (or requiring continued transfusion), where endoscopic and radiographic treatment has failed.

Key Points

  • Any patient with rectal bleeding required a flexible sigmoidoscopy or colonoscopy
  • A patient with a large fresh rectal bleed who is haemodynamically unstable has an upper GI bleed until proven otherwise
  • Acute bleeds may not initially show an anaemia in the full blood count
  • Patients who are haemodynamically unstable need an emergency OGD and colonoscopy