Reasoning GP · Algorithm · 1-page summary
Rectal bleeding in adults
For: adults (18 and over) with fresh PR bleeding, melaena, occult blood or haematochezia, in primary care. Not for: children. Known UC or Crohn's follows the specialist plan; upper GI symptoms with melaena are hospital-assessed.
Core rule: never attribute rectal bleeding to haemorrhoids before examination and the NG12 FIT criteria. Visible piles do not exclude a proximal cancer, and a FIT <10 does not exclude cancer when symptoms persist.
0Stop — call 999 now — before PR, FIT or bloods
- Shock, judged clinically (shock index HR/SBP >1 suggests it): pallor, cold peripheries, confusion, syncope → 999
- Profuse fresh rectal bleeding with instability, or melaena with haemodynamic compromise → 999
- Any GI bleeding after AAA repair: aortoenteric fistula until excluded (a herald bleed precedes exsanguination) → 999
- While waiting: the patient does not transfer independently. Do not delay transfer for a PR, FIT or bloods. Do not stop anticoagulation without specialist advice.
1Triage — stable patient: how much, and what kind?
| Bleeding | Action |
|---|---|
| Melaena, stable | Usually upper GI → Same-day A&E; hospital risk-stratifies and arranges endoscopy |
| Major or ongoing | Major or ongoing fresh bleed; significant bleed with major comorbidity or anticoagulation; acute bleed with significant anaemia → Same-day A&E |
| Minor, settled | Characterise, examine (block 3), apply NG12 (block 2) |
2Screen — NG12 colorectal cancer (updated April 2026)
- Offer FIT: unexplained rectal bleeding at ≥50; under 50 with bleeding plus unexplained abdominal pain or weight loss; change in bowel habit or iron-deficiency anaemia at any adult age; abdominal mass; anaemia at ≥60.
- FIT ≥10 µg Hb/g → Suspected cancer pathway
- Rectal mass, unexplained anal mass or unexplained anal ulceration → consider a Suspected cancer pathway referral; do not wait for FIT.
- Iron-deficiency anaemia + bleeding: a low FIT does not exclude; men and post-menopausal women generally need upper and lower GI assessment.
- FIT <10 with persistent or recurrent bleeding → still needs colorectal assessment; judgement can override a negative FIT.
- Acute severe UC (≥6 bloody stools a day + temperature >37.8°C, HR >90, Hb <105 g/L or ESR >30) → Same-day admission. Suspected new IBD, ischaemic colitis, recurrent significant diverticular bleeding → Urgent gastro
3Assess — stable patients only
☐ HR, BP lying and standing (systolic drop >20 mmHg = significant loss), temperature, RR, SpO₂, pallor ☐ Abdomen: mass, liver, tenderness ☐ Perianal inspection ☐ PR with consent and chaperone; proctoscopy for internal piles; too painful → document and arrange specialist assessment ☐ FBC, ferritin by indication; CRP and calprotectin only if IBD suspected; stool culture for acute bloody diarrhoea; rectal STI screen if possible
Do not repeat FIT to get a "normal", or use FIT to judge an acute bleed.
4Classify — only once block 2 is applied
- Haemorrhoids — bright red, on the paper, painless; internal piles need a proctoscope → block 5.
- Anal fissure — pain on defaecation, sentinel pile. Recurrent, lateral, multiple or non-healing → think Crohn's, cancer, infection, trauma.
- IBD or infective colitis — bloody diarrhoea, mucus, fever, travel; IBD commonest under 40 → stool tests, block 2.
- Diverticular or angiodysplasia — sudden, painless, large volume, older → hospital (block 1).
- Colorectal cancer — blood mixed with stool, change in habit, weight loss, tenesmus, anaemia → block 2.
- Uncertain — say so; apply the NG12 criteria and book review. Never default to "piles".
5Treat today — after cancer risk is assessed
- Haemorrhoids grade I–II: fibre, fluids, no straining; laxative by stool consistency; one topical steroid/anaesthetic preparation, about 5–7 days at most. Avoid codeine.
- Acute fissure: stool softening, fibre, fluids, analgesia, short topical anaesthetic. Persistent or chronic: GTN 0.4% (headache; not with PDE-5 inhibitors or hypotension) or diltiazem 2% (unlicensed, document consent) BD for about 8 weeks.
- Anticoagulant or NSAID: review NSAIDs; do not stop anticoagulation without specialist advice.
- Established UC: follow the specialist plan. Never treat undiagnosed bleeding as UC. Doses: NICE/SPC, BNF, local formulary.
6Refer routinely
- Grade III–IV haemorrhoids, or selected grade II → banding or surgery.
- Fissure not healed after 8 weeks of GTN or diltiazem → surgical (botulinum toxin, sphincterotomy). Complex fistula, rectal prolapse → colorectal.
- Rectal STI → sexual health. Check NHS bowel screening enrolment (from 50).
7Never reassure by
- Visible haemorrhoids, or bright red blood on the paper.
- A FIT <10 when bleeding persists or anaemia develops.
- A previous negative bowel-screening FIT in a symptomatic patient.
- Young age.
- Normal lying observations: check postural BP.
- Stool colour alone: a brisk upper GI bleed can present as fresh blood.
8Safety-net — say it, then document it
999 “Call 999 for heavy bleeding, collapse, feeling faint or dizzy with bleeding, vomiting blood, or severe tummy pain with bleeding.” Same-day “Black, tarry stools — go to A&E today. Bleeding that comes back heavily or has not settled after 48–72 hours, new weight loss or feeling unwell, or no cancer-pathway appointment arriving — contact us today.”
Follow-up: topical treatment reviewed at 1 week; FIT result actioned; fissure healing checked at 8 weeks. Persistent or recurrent bleeding → re-investigate, don't re-reassure.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Observations incl. postural BP normal
Abdomen, perianal and PR done (or reason recorded)
NG12 FIT criteria applied; result owner and date set
Safety-net given, including melaena and 999 words
Summary of the full Reasoning GP rectal bleeding algorithm, which holds the detail, examination, differentials and evidence. Sources: NICE NG12 (updated April 2026), HTG690, NG130, CG118; BSG lower GI bleeding (2019), iron-deficiency anaemia (2021) and BSG/ACPGBI FIT guidance. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.