Why Lower GI Bleeding Is Examined
Rectal bleeding is common in clinical practice — it affects up to 15% of the population at any time — but it is also an early warning sign of colorectal cancer, the fourth most common cancer in the UK. OSCEs examine it through history-taking stations (a 62-year-old presenting with rectal bleeding), communication stations (explaining a colonoscopy referral), and clinical reasoning. Examiners test systematic history-taking, correct application of NICE 2WW criteria, and appropriate investigation planning.
💡 Tip
Never assume rectal bleeding in an older patient is due to haemorrhoids without proper assessment. Haemorrhoids are common but so is colorectal cancer. Both can coexist — always perform a PR examination and consider sigmoidoscopy or colonoscopy based on the clinical picture.
Differential Diagnosis by Stool Character
| Appearance | Likely source | Differential |
|---|---|---|
| Bright red blood on the toilet paper only | Anal canal | Haemorrhoids, anal fissure |
| Bright red blood coating the stool | Rectum or sigmoid | Haemorrhoids, rectal carcinoma, polyps |
| Blood mixed throughout the stool | Left colon | Carcinoma, diverticular disease, inflammatory bowel disease |
| Dark red/maroon mixed stool | Right colon or brisk upper GI | Angiodysplasia, caecal carcinoma, brisk UGIB |
| Melaena (tarry, black) | Upper GI (above ligament of Treitz) | Peptic ulcer, varices, gastric cancer |
Systematic History — Key Questions
🧠 Mnemonic
COLOUR — rectal bleeding history:
- C haracter — bright red, dark red, maroon, melaena? Mixed with stool or on paper only?
- O nset — how long? First episode or recurrent?
- L oss — estimated volume? Clots? Toilet bowl red?
- O ther bowel symptoms — change in bowel habit (constipation, diarrhoea, alternating), tenesmus, incomplete emptying, mucus, flatus?
- U rge — any urgency, rectal pain, anal discomfort?
- R isk factors — age, family history of CRC/IBD, previous polyps, diet (low fibre), NSAIDs/anticoagulation
Associated systemic symptoms:
- Weight loss (unintentional — malignancy)
- Fatigue (iron deficiency anaemia)
- Abdominal pain (IBD, diverticulitis, malignancy)
- Fever (IBD flare, diverticulitis, infection)
- Travel history or dietary changes (infective cause)
Past medical history:
- Previous colonoscopy findings (polyps, diverticular disease)
- Inflammatory bowel disease (Crohn's, ulcerative colitis)
- Previous colorectal cancer or family history (Lynch syndrome, FAP)
- Liver disease (portal hypertension, anorectal varices)
- Coagulopathy, anticoagulants
NICE Two-Week Wait (2WW) Referral Criteria for Colorectal Cancer
Refer urgently (within 2 weeks) for suspected colorectal cancer if:
Age 40 and above:
- Rectal bleeding WITH change in bowel habit (looser stools and/or increased frequency) — for 6 weeks or more
- Change in bowel habit WITHOUT rectal bleeding (looser or more frequent stools) — for 6 weeks or more in adults over 40
Age 50 and above:
- Unexplained rectal bleeding
Any age:
- Positive faecal immunochemical test (FIT)
- Abdominal/rectal mass
- Unexplained iron deficiency anaemia (Hb below 110 g/L in men or below 100 g/L in post-menopausal women)
⚠️ Red Flag
Do not delay 2WW referral while treating presumed haemorrhoids. Haemorrhoidal treatment can be started but must not replace or delay urgent investigation for cancer when the clinical criteria are met.
Physical Examination
Abdominal Examination
- Inspect for distension, scars, stomas
- Palpate for masses (right iliac fossa — caecal carcinoma; left iliac fossa — diverticular disease, sigmoid carcinoma)
- Signs of peritonism (diverticulitis perforation)
PR Examination — Essential in All Rectal Bleeding
- Inspect: skin tags, external haemorrhoids, fissure, fistula opening, perianal disease (Crohn's)
- Digital examination: resting tone, sphincter squeeze, mucosal surface (feel for polyp or low rectal tumour), prostate (men), cervix/pouch of Douglas (women)
- Result: note any mass, tenderness, blood on the glove, mucus
💎 Clinical Pearl
A PR examination is mandatory in all rectal bleeding presentations. Never complete a lower GI bleeding history without performing or stating that you would perform a PR examination. Up to 10% of rectal cancers are palpable on digital examination.
Investigation Pathway
| Situation | Investigation |
|---|---|
| 2WW criteria met | Urgent colonoscopy (or CT colonography if colonoscopy declined) |
| Bright red PR bleeding, age below 40, typical haemorrhoidal history | Rigid or flexible sigmoidoscopy |
| Suspected IBD | Colonoscopy + biopsies + faecal calprotectin + inflammatory markers |
| Suspected diverticulitis (LIF pain + PR bleeding + fever) | CT abdomen/pelvis with contrast |
| Acute massive lower GI bleeding (haemodynamic compromise) | CT angiography (detects active bleeding at 0.5 mL/min); interventional radiology embolisation |
| Iron deficiency anaemia + PR bleeding | Upper GI endoscopy + colonoscopy (bidirectional) |
| FIT test (primary care) | Low risk screening — positive result: urgent colonoscopy |
Causes by Age Group
| Age group | Common causes |
|---|---|
| Under 30 | Haemorrhoids, anal fissure, IBD, infective colitis, polyps |
| 30-50 | IBD, haemorrhoids, diverticular disease, colorectal polyps/carcinoma beginning |
| Over 50 | Colorectal carcinoma, diverticular disease, haemorrhoids, angiodysplasia |
| Any age | Infective colitis (Campylobacter, Salmonella, EHEC), antibiotic-associated colitis (C. difficile) |
Frequently Asked Questions
"What is the FIT (faecal immunochemical test) and how is it used?"
FIT detects human haemoglobin in stool using a monoclonal antibody. In primary care, it is used as a triage tool in patients with symptoms not meeting immediate 2WW criteria — a positive FIT (above 10 micrograms/g faeces) triggers urgent colonoscopy referral. In the NHS Bowel Cancer Screening Programme, FIT has replaced guaiac-based FOB testing as the standard screening method for adults aged 50-74. FIT is more sensitive and specific for colorectal cancer than guaiac testing.
"What is the difference between diverticulosis and diverticulitis?"
Diverticulosis is the presence of mucosal outpouchings (diverticula) in the colon — present in over 50% of people above age 60. Most are asymptomatic. Diverticulitis is inflammation or infection within a diverticulum, causing left iliac fossa pain, fever, and raised inflammatory markers. Diverticular bleeding (diverticulosis + bleeding from an eroded artery) is the most common cause of significant lower GI bleeding in older adults — typically painless, bright red, and self-limiting.
"How do you differentiate Crohn's disease from ulcerative colitis on history?"
UC is confined to the colon (continuous from rectum), presents with bloody diarrhoea, rectal urgency, and tenesmus. Crohn's can affect any part of the GI tract (mouth to anus), with skip lesions; features include abdominal pain, non-bloody diarrhoea, perianal disease (fistulae, abscesses, skin tags), and extraintestinal manifestations. Both can cause rectal bleeding — UC more commonly. PR examination revealing perianal disease strongly favours Crohn's.
"What is angiodysplasia and when should it be suspected?"
Angiodysplasia (arteriovenous malformations of the colon wall) is the most common cause of lower GI bleeding in the elderly, particularly those with aortic stenosis (Heyde's syndrome — acquired von Willebrand factor deficiency). Features: painless intermittent rectal bleeding or occult blood loss causing iron deficiency anaemia; typically affects the right colon (caecum, ascending colon). Diagnosis: colonoscopy (cherry-red vascular lesion) or CT angiography during active bleeding. Treatment: endoscopic argon plasma coagulation.
"What are Lynch syndrome and FAP, and when should they be suspected?"
Lynch syndrome (HNPCC — hereditary non-polyposis colorectal cancer) is an autosomal dominant mismatch repair gene defect (MLH1, MSH2, MSH6, PMS2). Risk: 50-80% lifetime CRC risk; also endometrial, ovarian, urinary tract cancers. Amsterdam II criteria: 3 affected relatives, 2 successive generations, 1 below age 50, FAP excluded. Familial adenomatous polyposis (FAP) causes hundreds to thousands of colonic polyps from adolescence — 100% cancer risk without colectomy (APC gene mutation). Suspect FAP in rectal bleeding in a young patient with a personal or family history of multiple polyps.
Related Posts
- Abdominal Examination OSCE — palpating for abdominal masses and tenderness
- PR Rectal Examination OSCE — technique and findings in the rectal examination
- Upper GI Bleeding OSCE — differentiating upper from lower GI haemorrhage