Based on practical application of guidance from National Institute for Health and Care Excellence (NICE) and usual NHS gastro pathways — simplified into:

👉 what to test first
👉 who needs colonoscopy
👉 who doesn’t need referral

Because the two biggest real-life mistakes are:

❌ scoping everyone
❌ labelling IBS too early

This pathway helps you avoid both.

✅ Why this matters

Chronic diarrhoea is one of the most common gastro referrals.

Most cases are:

IBS
functional
benign

But some are:

IBD
coeliac
cancer
microscopic colitis

Your job is:

rule out serious disease safely
without over-investigating everyone

✅ First principle

Always ask:

Are there red flags?

Because:

Red flags → urgent investigation
No red flags → basic tests first

Never jump straight to colonoscopy.

🚨 Step 1 – Screen for red flags FIRST

If any of these are present, skip routine tests and escalate early.

Red flags

Weight loss
Rectal bleeding
Iron deficiency anaemia
Nocturnal diarrhoea
Persistent severe pain
Fever
Raised CRP
Family history colorectal cancer/IBD
Age >50 with new symptoms

👉 These patients usually need urgent colonoscopy (2WW or early referral)

Do not label IBS.

✅ Step 2 – Characterise the diarrhoea (quick clinical clues)

This often narrows the cause before tests.

Watery

→ IBS, bile acid diarrhoea, drugs

Bloody/mucus

→ IBD, infection, cancer

Greasy/floating

→ malabsorption, pancreatic

Nocturnal

→ organic (not IBS)

Post-meal urgency

→ IBS or bile acid diarrhoea

History is high yield — don’t skip it.

✅ Step 3 – First-line tests (for almost everyone)

These should be done before referral in most stable patients.

Bloods

FBC
U&E
CRP
LFTs
Coeliac screen (tTG-IgA)
TFTs

Stool tests

Stool culture (if infection possible)
C. diff (recent antibiotics/admission)
Faecal calprotectin (very important)

Calprotectin is key for separating:
👉 IBS vs IBD

✅ Step 4 – Use results to guide next step

This is where the pathway becomes simple.

🟢 Normal tests + normal calprotectin

Likely:
👉 IBS / functional diarrhoea

Management:

no colonoscopy
conservative treatment

Most patients fall here.

🔴 Raised calprotectin or CRP

Think:
👉 IBD

Next step:
👉 colonoscopy with biopsies

🔴 Iron deficiency anaemia

Think:
👉 malignancy until proven otherwise

Next step:
👉 colonoscopy ± OGD

🟡 Positive coeliac screen

Next step:
👉 OGD with duodenal biopsy

🟡 Persistent unexplained diarrhoea (>6–8 weeks) despite normal tests

Consider:
👉 routine colonoscopy (microscopic colitis etc.)

🟡 Fatty stools/weight loss

Consider:
👉 pancreatic insufficiency → faecal elastase

✅ Step 5 – Common diagnoses you’ll actually see

Focus on realistic NHS cases.

Most common

IBS
Bile acid diarrhoea
Coeliac disease
IBD
Medication side effects (metformin, PPIs, antibiotics)

Less common but important

Microscopic colitis
Pancreatic insufficiency
Cancer

Don’t chase rare zebras early.

✅ Practical ward/clinic examples

Scenario 1

Young patient, normal bloods, calprotectin normal
→ IBS
→ no scope

Scenario 2

Chronic diarrhoea + raised calprotectin
→ colonoscopy (IBD likely)

Scenario 3

IDA + diarrhoea
→ urgent GI workup

Scenario 4

Watery diarrhoea, normal tests, older patient
→ consider microscopic colitis → colonoscopy

Scenario 5

Greasy stools + weight loss
→ pancreatic tests

✅ When to refer to gastro

Refer if:

red flags
raised calprotectin
anaemia
suspected IBD
coeliac positive
persistent unexplained symptoms

Do not refer straightforward IBS.

❌ Common junior mistakes

Scoping everyone immediately
Forgetting calprotectin
Missing coeliac screen
Labeling IBS without tests
Ignoring medications
Not checking red flags

Be systematic — it saves unnecessary scopes.

✅ Simple NHS pathway (easy memory rule)

Think:

1️⃣ Red flags? → scope
2️⃣ Basic bloods + stool tests
3️⃣ Calprotectin result
4️⃣ Normal → IBS
5️⃣ Abnormal → investigate

That’s 95% of cases.

✅ Take-home concept

Most chronic diarrhoea is IBS.
Your job is to safely exclude IBD, cancer, and coeliac — then stop investigating.

Over-testing causes more harm than good.