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Health condition

Lower intestinal bleeding, why it happens and how it's found and stopped.

Blood from the back passage is common and often minor - but it always deserves an answer. Here's how UK teams work out why, and what to do if it's heavy.

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Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against NICE and British Society of Gastroenterology (BSG) sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice including early colonoscopy, CT angiography and endoscopic haemostasis.

Key facts

Lower intestinal bleeding at a glance.

The essentials, in plain English - what it means, why it happens, and how it's investigated in the UK today.

  • What it is

    Bleeding from the colon, rectum or anus - anywhere distal to the ligament of Treitz, the anatomical marker between the upper and lower gut.

  • Most common cause

    Diverticular disease is the leading cause of significant lower GI bleeding in UK adults, though it usually stops on its own.

  • Two patterns

    Bright red or maroon blood (haematochezia) usually means a lower source; black, tarry stool (melaena) usually points higher up the gut.

  • Who is at risk

    Older adults, people on anticoagulants or antiplatelets, and anyone with diverticular disease, piles, polyps or inflammatory bowel disease.

  • Key investigation

    Colonoscopy is the investigation of choice once you are stable - it finds the source and can treat it in the same procedure.

  • When it is urgent

    Heavy, ongoing bleeding with a fast heart rate, dizziness or fainting is a medical emergency - call 999 or go to A&E.

Why this guide matters

A wide range of causes, a clear pathway.

Lower GI bleeding runs from a harmless anal fissure to a genuine emergency. The three points below shape how it's assessed and treated.

  • Most causes are manageable

    Piles, small fissures and self-limiting diverticular bleeds account for the majority of cases seen in UK primary and secondary care.

  • Severity dictates the pathway

    A stable, minor bleed is worked up routinely. Heavy or ongoing bleeding with instability is resuscitated first, investigated second.

  • Colonoscopy usually gives the answer

    It finds the source in most cases and can treat many of them - clips, adrenaline injection or thermal therapy - in the same sitting.

How the diagnosis is made

From first bleed to a confirmed source.

The steps a UK emergency department, GP or gastroenterology team will normally follow, per NICE and BSG guidance.

  1. 01

    Assessing

    History and medicines review

    When bleeding started, how much, colour and pattern, plus a check for anticoagulants, aspirin and NSAIDs.

  2. 02

    Assessing

    Examination and PR exam

    A rectal examination confirms the bleeding, checks for piles or a fissure, and assesses how unwell you are.

  3. 03

    Assessing

    Haemodynamic assessment

    Pulse, blood pressure and a shock index flag anyone who needs immediate resuscitation rather than routine tests.

  4. 04

    Confirming

    Bloods: FBC, clotting, group and save

    Full blood count, coagulation screen and group and save (or crossmatch) in case transfusion is needed.

  5. 05

    Confirming

    Colonoscopy once stabilised

    The investigation of choice for most lower GI bleeding - it locates the source and can stop it there and then (see /treatments/colonoscopy/).

  6. 06

    Confirming

    CT angiography if bleeding is brisk

    For severe or ongoing bleeding where colonoscopy is not immediately possible or the source is unclear, CT angiography finds active bleeding fast.

  7. 07

    Escalating

    Capsule endoscopy if still unclear

    If colonoscopy and gastroscopy are both negative, a capsule endoscopy looks at the small bowel in between.

  8. 08

    Escalating

    Specialist MDT input

    Gastroenterology, colorectal surgery and interventional radiology work together on anything beyond straightforward cases.

Typical timeline: immediate resuscitation if unstable, then colonoscopy once safe - often within 24 to 48 hours.

Symptoms

What lower GI bleeding looks like.

Blood can be obvious or hidden, painful or painless. The features below help distinguish routine causes from ones that need urgent care.

  • Bright red blood (haematochezia)

    Fresh red blood in or on the stool, on the toilet paper, or dripping into the pan - usually from the colon, rectum or anus.

  • Black, tarry stool (melaena)

    Sticky, very dark, strong-smelling stool that can mean a brisk lower bleed as well as an upper GI source.

  • Abdominal pain

    Present in some causes such as ischaemic colitis or infective colitis, but often completely absent with diverticular bleeding or piles.

  • Dizziness or fainting

    A sign of significant blood loss and a drop in blood pressure - treat as an emergency.

  • A racing heart or clamminess

    The body compensating for blood loss - along with pale skin, this needs urgent assessment.

  • Tiredness and breathlessness

    Chronic, low-level bleeding can cause iron deficiency anaemia over weeks or months, often without obvious visible blood (see /conditions/iron-deficiency-anemia/).

  • Change in bowel habit

    New looseness, urgency or altered stool shape alongside bleeding can point to inflammatory bowel disease or, less commonly, a tumour.

  • Red flag: heavy or ongoing bleeding

    Continuous bleeding, large volumes, or bleeding with fainting or a racing pulse needs 999 or immediate A&E attendance.

Causes

Why lower GI bleeding happens.

Some causes are common and usually minor; others are rarer but need specific investigation and treatment.

  • Diverticular disease

    The most common cause of significant lower GI bleeding - small pouches in the colon wall that can bleed suddenly, often without pain.

  • Haemorrhoids (piles)

    Usually minor, bright red bleeding on wiping or in the pan - the most frequent cause of rectal bleeding overall.

  • Colorectal cancer and polyps

    A key reason new bleeding needs investigation, particularly over 50 (see /conditions/colon-cancer/).

  • Angiodysplasia

    Small, fragile blood vessel abnormalities in the bowel wall, more common in older adults and a cause of recurrent bleeding.

  • Inflammatory bowel disease

    Ulcerative colitis and Crohn’s disease can both cause bleeding as part of a flare (see /conditions/inflammatory-bowel-disease/, /conditions/ulcerative-colitis/, /conditions/crohns-disease/).

  • Ischaemic colitis

    Reduced blood flow to part of the colon, often with pain, more common in older adults with vascular disease (see /conditions/ischemic-colitis/).

  • Infective colitis

    Bacterial or other infections of the colon causing bleeding, diarrhoea and sometimes fever.

  • Anal fissure

    A small tear in the anal lining, usually causing pain and bright red blood, often related to constipation.

  • Radiation proctitis

    Bleeding from the rectum following pelvic radiotherapy, sometimes appearing months or years afterwards.

Treatment

How lower GI bleeding is treated in the UK.

Resuscitation first if you are unwell, then endoscopic, radiological or surgical control of the bleeding, followed by treating the underlying cause.

  • Resuscitation first

    IV access, fluids and, where needed, blood products - always the first step in anyone bleeding heavily. This is an emergency, not a wait-and-see situation.

  • Reversing anticoagulation

    Warfarin, DOACs or antiplatelets are reviewed and, where clinically appropriate, reversed or paused under specialist guidance.

  • Endoscopic haemostasis

    Clips, adrenaline injection or thermal (heater probe) therapy applied at colonoscopy to seal the bleeding point directly.

  • Interventional radiology embolisation

    For bleeding that endoscopy cannot reach or control, a radiologist blocks the feeding blood vessel from inside using a catheter (see /treatments/mesenteric-artery-stenting/).

  • Surgery

    Reserved for uncontrolled haemorrhage, perforation or bleeding that other methods cannot stop - now uncommon thanks to endoscopic and radiological options.

  • Treating the underlying cause

    Diverticular disease, colorectal cancer, IBD, haemorrhoids or ischaemic colitis each need their own long-term management plan once the bleeding is controlled.

  • Iron replacement

    IV or oral iron for anaemia caused by chronic or recurrent blood loss - IV iron therapy works faster when levels are low or oral iron is not tolerated (see /treatments/iv-iron-therapy/).

  • Specialist MDT follow-up

    Ongoing joint input from gastroenterology, colorectal surgery and interventional radiology for anyone with recurrent or hard-to-source bleeding.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or gastroenterology team knows your history and can tell you which parts apply to you. If bleeding is heavy, don't wait - get seen.

  • NICE. Gastrointestinal bleeding: clinical guidance and referral pathways.

  • British Society of Gastroenterology (BSG). Guidelines on the management of acute lower gastrointestinal bleeding.

  • NICE. Colorectal cancer: recognition and referral (NG12) - red flags relevant to rectal bleeding.

  • MHRA and BSG. Guidance on anticoagulant and antiplatelet management around GI bleeding and endoscopy.

Red flags

When lower GI bleeding needs urgent attention.

Most bleeding is minor and manageable. These are the situations that aren't - and where emergency or urgent care is needed.

  • Heavy, ongoing bleeding

    Continuous fresh bleeding or repeated large-volume bleeds needs a 999 call or immediate A&E attendance - do not wait for a GP appointment.

  • Fainting, dizziness or a racing pulse

    Signs of significant blood loss affecting your circulation. Treat as an emergency and seek urgent care.

  • Bleeding on anticoagulants

    Warfarin, apixaban, rivaroxaban and similar drugs increase both the risk and the severity of GI bleeding - always seek urgent assessment.

  • New bleeding over the age of 50

    Rectal bleeding in this age group, especially with a change in bowel habit or weight loss, needs prompt investigation to rule out colorectal cancer.

  • Bleeding with severe abdominal pain

    Can suggest ischaemic colitis or a more serious underlying cause and needs same-day medical review.

  • Unexplained iron deficiency anaemia

    Low iron with no obvious cause deserves investigation for an occult lower (or upper) GI source, even without visible bleeding.

  • Bleeding with fever and diarrhoea

    Can indicate infective colitis or a flare of inflammatory bowel disease - needs prompt assessment and stool testing.

  • Persistent bleeding after a colonoscopy

    Any bleeding that continues or restarts after an endoscopic procedure needs immediate reporting to the team who performed it.

  • Bleeding in pregnancy

    Rectal bleeding in pregnancy is usually from piles but still warrants a clinical review to rule out other causes.

Living with it

Manageable for most, with the right vigilance.

Four things that make the biggest difference - knowing your own pattern, handling medicines carefully, looking after your gut, and knowing when to act.

A quiet reminder

New bleeding is never something to just watch and wait on.

Even when it turns out to be minor, getting it checked rules out the causes that matter most.

  1. 01 Know it

    Learn your own pattern

    Occasional spotting from known piles is different from a new, heavier or painless bleed - know what is usual for you and what is not.

  2. 02 Medicines

    Never stop anticoagulants alone

    If you are on blood thinners and notice bleeding, contact your GP or the anticoagulation clinic rather than stopping the medicine yourself.

  3. 03 Diet

    Support your gut day to day

    A high-fibre diet and good hydration help manage diverticular disease and piles, the two most common lower-level causes.

  4. 04 Escalate

    When in doubt, get checked

    New or unexplained bleeding, at any age, is worth a GP appointment - and heavy or ongoing bleeding is worth 999 or A&E.

Frequently asked

Everything we get asked about lower GI bleeding.

Quick answers on causes, colonoscopy, and when bleeding is an emergency.

  • What counts as lower intestinal bleeding?

    It means bleeding from anywhere distal to the ligament of Treitz - the colon, rectum or anus - as opposed to upper GI bleeding from the stomach or oesophagus. It can show up as bright red blood, maroon stool, or occasionally as melaena if the bleeding is brisk.

  • What is the most common cause?

    Diverticular disease is the most common cause of significant lower GI bleeding in the UK, particularly in older adults. Most diverticular bleeds settle on their own, but they still need proper assessment because they can recur.

  • Is rectal bleeding always serious?

    No - most cases are due to haemorrhoids (piles) or a small anal fissure and are minor. But new bleeding, especially over the age of 50, with a change in bowel habit, weight loss or heavy volume, needs prompt medical assessment to rule out more serious causes such as colorectal cancer.

  • Why does colonoscopy matter so much?

    Colonoscopy is the investigation of choice once you are stable because it can see directly into the colon, find the source of bleeding, and treat many causes - such as with clips or adrenaline injection - in the same procedure.

  • What should I do if bleeding is heavy?

    Heavy or ongoing bleeding, especially with dizziness, a racing heart or fainting, is a medical emergency. Call 999 or go to your nearest A&E rather than waiting to see your GP.

  • Can lower GI bleeding cause anaemia without obvious blood loss?

    Yes. Slow, chronic or intermittent bleeding from causes such as diverticular disease, colorectal polyps or angiodysplasia can cause iron deficiency anaemia with tiredness and breathlessness, even when you have not noticed any visible blood.

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