About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Lower GI bleed = distal to ligament of Treitz. Presents with haematochezia (fresh red blood PR) or maroon stools
- Commonest causes: diverticular disease (most common in over-60s), haemorrhoids, colorectal cancer, IBD, angiodysplasia
- Massive lower GI bleed: ABCDE resuscitation → consider OGD first (to exclude upper GI source) → then colonoscopy or CT angiography
- Most diverticular bleeds (~80%) stop spontaneously; persistent bleeding requires CT angiography ± embolisation or surgery
- Always exclude colorectal malignancy in anyone ≥40 with unexplained rectal bleeding — FIT and/or colonoscopy
Overview
Lower GI bleeding originates from the colon, rectum, or anal canal (distal to the ligament of Treitz). It accounts for approximately 20–30% of significant GI haemorrhage. The most common cause in older adults is diverticular disease, while in younger patients inflammatory bowel disease and infectious colitis predominate. Other causes include angiodysplasia, colorectal polyps/cancer, ischaemic colitis, haemorrhoids, anal fissures, and radiation proctitis. Approximately 80–85% of lower GI bleeds stop spontaneously.
Epidemiology
Lower GI bleeding is responsible for approximately 20,000 hospital admissions per year in the UK. Incidence increases with age, particularly beyond 60 years. Diverticular bleeding is the commonest cause of major lower GI haemorrhage (30–40%). Colorectal cancer accounts for approximately 5–10% of cases of rectal bleeding investigated in secondary care. Mortality from major lower GI bleeding is approximately 2–4%, lower than for upper GI bleeding.
Clinical Features
Symptoms
Fresh red blood per rectum (haematochezia) — on paper, in pan, or mixed with stool
Dark red or maroon stool (proximal colonic source)
Painless massive rectal bleeding (diverticular bleed or angiodysplasia)
Change in bowel habit with bleeding (raises suspicion of colorectal cancer)
Bloody diarrhoea with urgency (IBD, infective colitis)
Perianal pain with bleeding (anal fissure, thrombosed haemorrhoid)
Weight loss with rectal bleeding
Signs
Fresh blood on digital rectal examination (DRE)
Palpable rectal mass on DRE
Haemodynamic instability in major haemorrhage (tachycardia, hypotension)
Abdominal tenderness (ischaemic colitis, IBD flare)
Perianal abnormalities: fissure, haemorrhoids, fistula
Pallor and signs of iron deficiency anaemia
Investigations
First-line
FBC, U&Es, coagulation, group and crossmatchAssess blood loss severity and coagulopathy. Hb may be initially normal in acute bleed
Digital rectal examination and proctoscopyEssential — assess for haemorrhoids, fissure, rectal mass, blood colour
FIT (faecal immunochemical test)Quantitative FIT ≥10 µg Hb/g faeces → 2-week-wait referral for suspected colorectal cancer (NICE NG12)
Second-line
ColonoscopyGold standard investigation for non-acute lower GI bleeding — diagnostic and therapeutic. Perform after bowel prep
CT angiography (triple phase)In acute massive bleeding — can identify active extravasation if bleeding rate >0.5 mL/min. Guides embolisation
Flexible sigmoidoscopyIf left-sided source suspected or colonoscopy not possible
Specialist
Mesenteric angiography and embolisationFor ongoing bleeding identified on CTA — allows superselective embolisation
Technetium-99m red blood cell scanDetects slower intermittent bleeding (>0.1 mL/min) — useful if CTA negative but ongoing bleeding
Capsule endoscopyIf bleeding source not identified on OGD and colonoscopy — investigate small bowel (obscure GI bleeding)
1
Resuscitation (if major bleed)
- ABCDE approach, 2 × large-bore IV cannulae, crystalloid resuscitation
- Crossmatch and transfuse PRBCs if Hb <70 g/L (target 70–90 g/L)
- Correct coagulopathy (FFP, platelets, vitamin K as needed)
- Consider OGD first to exclude brisk upper GI source (up to 15% of haematochezia is from upper GI)
2
Investigation strategy
- Minor self-limiting bleed: outpatient investigation with colonoscopy or flexible sigmoidoscopy
- Major bleed not settling: urgent CT angiography to localise bleeding point
- Stable major bleed: inpatient colonoscopy within 24 hours (after bowel prep if feasible)
3
Definitive management
- Diverticular bleed: most stop spontaneously; endoscopic haemostasis if active source identified; embolisation or segmental colectomy if refractory
- Angiodysplasia: argon plasma coagulation (APC) at colonoscopy
- Colorectal cancer: staging and MDT referral
- IBD: treat flare with corticosteroids and disease-modifying therapy
- Haemorrhoids/fissure: conservative management (see separate entries)
Complications
- Hypovolaemic shock: From massive diverticular or angiodysplastic bleeding
- Missed malignancy: Attributing rectal bleeding to haemorrhoids without investigating — always consider colonoscopy in patients ≥40
- Recurrent bleeding: Diverticular bleeds recur in ~25% within 4 years; angiodysplasia often recurrent
- Iron deficiency anaemia: From chronic occult lower GI blood loss — requires investigation
UKMLA Exam Tips
- 1Up to 15% of haematochezia is from a BRISK upper GI source — always consider OGD if haemodynamically significant
- 2Painless massive rectal bleeding in elderly = diverticular bleed until proven otherwise
- 3Angiodysplasia: commonest cause of obscure GI bleeding in elderly. Associated with aortic stenosis (Heyde syndrome) and CKD
- 4FIT ≥10 µg Hb/g faeces = 2WW referral for colorectal cancer (NICE NG12/DG56)
- 5Never attribute rectal bleeding solely to haemorrhoids without excluding proximal pathology (especially age ≥40 or red flags)
practicetest your knowledge on lower gi bleedApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — gastroenterology and beyond.
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