Indications for Colonoscopy

Colonoscopy is one of the most commonly requested investigations in gastroenterology.

It is excellent for:

  • Cancer detection
  • IBD diagnosis
  • Bleeding sources
  • Polyp removal

But it is:

  • Invasive
  • Resource-limited
  • Not risk-free

So the key question is:

Who truly needs colonoscopy, and how urgently?

This guide focuses on safe, practical decision-making for junior doctors in everyday NHS practice.

✅ First principle

Before requesting colonoscopy, ask:

Will this change management?

If the result won’t alter what you do → don’t scope.

Colonoscopy is not a screening test for vague symptoms.

🚨 URGENT / INPATIENT COLONOSCOPY (same admission)

These patients usually need early inpatient or urgent investigation.

🔴 Acute lower GI bleeding

  • PR bleeding
  • Haematochezia
  • Hb drop
  • Ongoing bleeding

Because:

  • May need endoscopic therapy
  • Need to identify source (diverticular, angiodysplasia, tumour)

👉 Early colonoscopy once stable and prepped

If unstable → CT angiography first

🔴 Suspected acute severe colitis (IBD flare)

  • Bloody diarrhoea
  • Raised CRP
  • Systemically unwell

Because:

  • Need confirmation
  • Guide steroids/biologics

👉 Flexible sigmoidoscopy initially (often safer than full colonoscopy)

Important nuance:
👉 Not always full colonoscopy in severe colitis

🔴 Suspected colorectal cancer with obstruction

  • Change in bowel habit
  • Weight loss
  • Anaemia
  • Obstructive symptoms

Often:

  • CT first
  • Urgent scope pathway

🔴 Severe unexplained colitis / ischaemic colitis

Diagnostic colonoscopy needed during admission.

⚠️ URGENT OUTPATIENT (2-week wait cancer pathway)

Very common and high-yield.

These should not wait months.

🟡 Iron deficiency anaemia (very important)

Especially:

  • Men
  • Postmenopausal women

Because:

GI cancer until proven otherwise

👉 Colonoscopy ± OGD

One of the most common indications in the NHS.

🟡 Rectal bleeding with red flags

Bleeding PLUS:

  • Weight loss
  • Anaemia
  • Change in bowel habit
  • Age >50–60

👉 Urgent pathway

🟡 Change in bowel habit (persistent)

Especially:

  • New onset
  • Older patients
  • Looser stools
  • Increased frequency

Think malignancy first.

🟡 Positive FIT test

Common via GP pathway.

Requires colonoscopy.

🟡 Suspected IBD (new diagnosis)

  • Chronic diarrhoea
  • Raised calprotectin
  • Weight loss
  • Blood/mucus

Needs colonoscopy + biopsies

✅ ROUTINE / ELECTIVE COLONOSCOPY

Appropriate but not urgent.

🟢 Chronic diarrhoea (non-acute)

After:

  • Basic bloods
  • Stool tests
  • Coeliac screen
  • Calprotectin

If still unexplained → routine colonoscopy

🟢 Surveillance

  • Previous polyps
  • IBD surveillance
  • Family history
  • Post-cancer follow-up

Planned, not urgent.

🟢 Unexplained abdominal symptoms after basic workup

Selected cases only.

❌ Usually NO colonoscopy needed

Very common over-referrals.

❌ Young patient with obvious haemorrhoids and bright red PR bleed

Often:

  • PR exam
  • Conservative management

Not everyone needs colonoscopy

❌ IBS with normal tests and no red flags

Normal bloods + normal calprotectin + typical IBS
→ no scope

❌ Mild constipation alone

Treat first

❌ Acute infectious diarrhoea

Usually stool tests, not colonoscopy

✅ Red flags that should trigger colonoscopy thinking

If present, escalate urgency:

  • Iron deficiency anaemia
  • Persistent rectal bleeding
  • Weight loss
  • Change in bowel habit
  • Palpable mass
  • Family history CRC
  • Raised calprotectin
  • Age >50 with new symptoms

These are cancer/IBD until proven otherwise.

✅ Practical ward decision rule

When thinking about colonoscopy:

Ask:

  1. Bleeding?
  2. Cancer red flags?
  3. Suspected IBD?
  4. Failed basic workup?

If yes → scope
If no → manage conservatively first

Simple and safe.

✅ Colonoscopy vs flexible sigmoidoscopy (quick tip)

Flexible sig:

  • Acute colitis
  • Quick inpatient assessment
  • Safer in severe inflammation

Full colonoscopy:

  • Cancer workup
  • Chronic symptoms
  • Surveillance

Important on-call distinction.

✅ How to make a good colonoscopy referral

Include:

  • Exact indication
  • Symptoms duration
  • Hb
  • FIT/calprotectin results
  • Stability
  • Comorbidities
  • Anticoagulation

Clear indications → faster scopes.

❌ Common junior mistakes

  • Scoping IBS without red flags
  • Missing iron deficiency anaemia
  • Forgetting FIT/calprotectin first
  • Not examining for haemorrhoids
  • Referring without basic workup
  • Doing full colonoscopy in severe colitis

Use colonoscopy thoughtfully.

✅ Take-home concept

Scope bleeding, red flags, cancer suspicion, and IBD.
Don’t scope simple IBS or minor symptoms.
Investigate logically before referring.