Colorectal cancer is the 4th most common cancer in the UK (~43,000/year) and the 2nd most common cause of cancer death. NICE NG12 data shows that 10% of patients with unexplained rectal bleeding referred via 2WW have colorectal cancer. Critically, haemorrhoids are present in 40% of the population — the dangerous error is attributing bleeding to haemorrhoids without excluding more serious pathology. Upper GI bleeding presenting as melaena has 10% in-hospital mortality — time to endoscopy is directly correlated with outcomes (Glasgow-Blatchford score drives urgency). Never assume bright red blood = haemorrhoids alone without appropriate assessment.

The colour and distribution of blood is the single most important clinical discriminator. Bright red blood on the paper or separate from stool (rather than mixed) has a positive predictive value of 85% for an anorectal source. However — this still leaves 15% with more proximal pathology. Melaena occurs with as little as 50–80ml of blood from any source above the ileocaecal valve, and requires >14h transit time to oxidise haemoglobin to haematin. NSAIDs double the risk of diverticular bleeding — and anticoagulants quadruple it. Always ask about medication.

Diverticular bleeding is the most common cause of significant lower GI haemorrhage in adults over 50, accounting for 30–40% of hospitalised LGI bleeds. It is almost always painless and stops spontaneously in 80% of cases — but requires hospital assessment for transfusion and colonoscopy. Aortoenteric fistula is rare but uniformly fatal without immediate surgery — any patient with prior AAA repair presenting with GI bleeding must be treated as this until excluded. IBD first presentation in primary care is frequently delayed by an average of 2 years — think of it in any young adult with bloody diarrhoea.

PR examination detects rectal cancers within 8cm of the anal verge — approximately 30% of colorectal cancers are within reach of the examining finger. Failure to perform a PR examination in a patient with rectal bleeding is a significant clinical and medicolegal failure. Internal haemorrhoids (the most common cause of bright PR bleeding) cannot be seen or felt on PR exam alone — they require proctoscopy. Postural drop (orthostatic hypotension) identifies occult haemodynamic compromise in patients appearing well supine — check it in any patient with significant rectal bleeding.

FIT (faecal immunochemical test) has replaced FOBT (faecal occult blood test) as the preferred primary care investigation. FIT is more sensitive (specificity 94%, sensitivity 74% for CRC at threshold 10 µg/g) and specific — it detects human haemoglobin, not animal blood in food. NICE DG30 recommends FIT to guide colonoscopy need in symptomatic patients. However, in patients with overt rectal bleeding meeting 2WW criteria, FIT should not delay referral — a negative FIT does NOT exclude CRC in this group. Faecal calprotectin has 93% sensitivity for IBD — it is the recommended primary care test before gastroenterology referral (BSG and NICE CG61).

NICE NG12 deliberately sets a low threshold for 2WW rectal bleeding referral — the positive predictive value for CRC in referred patients is only 5–10%, meaning 90-95% will have a benign cause. This is intentional: missing CRC carries far greater harm than an unnecessary colonoscopy. The Glasgow-Blatchford score is the validated tool for risk-stratifying upper GI bleeds: score ≥6 predicts need for intervention (endoscopy, blood, surgery) with 99% sensitivity. Grade III haemorrhoids (require manual reduction) and grade IV (irreducible) almost always need surgical referral — topical treatment is ineffective at this stage.

GTN 0.4% ointment works by relaxing the internal anal sphincter (reducing hypertonia that impairs fissure healing) — it achieves 60–70% healing rate vs 40% for lidocaine alone. Diltiazem 2% cream has equivalent efficacy but fewer side effects — recommended if GTN causes intolerable headaches. Rubber band ligation for haemorrhoids has 80% success rate and is significantly more effective than injection sclerotherapy (Cochrane review). Topical steroids should not be used for more than 7 days continuously (atrophy, infection risk). Stopping NSAIDs in diverticular disease reduces re-bleed risk by 2–3 fold.

A high-fibre diet reduces haemorrhoid recurrence by 50% and diverticular bleed recurrence by 40% — this is level 1 evidence. Physical activity reduces colorectal cancer risk by 30–40% across multiple meta-analyses — comparable to the impact of aspirin chemoprevention but without the bleeding risk. NHS Bowel Cancer Screening (FIT programme) has 25% mortality reduction in screened populations — ensuring eligible patients are enrolled and engaged is a primary care quality metric. Alcohol is a recognised WHO Group 1 carcinogen for colorectal cancer — clear, quantified advice should be given at every opportunity.

Patients with adenomas found on colonoscopy have a 3–5× increased risk of future CRC — surveillance intervals (BSG 2019 guidelines) are evidence-based and must be communicated clearly and followed up. IBD patients with pancolitis for >8 years have 2% annual risk of CRC — annual surveillance colonoscopy is mandatory. Patients who do not receive their 2WW appointment confirmation within 14 days should be followed up proactively — system failures occur, and the patient cannot always advocate for themselves. A documented safety-net discussion is an RCGP SCA examination competency requirement.