Chronic diarrhoea is defined as:

Loose stools for >4 weeks

It is a very common referral to gastro and clinics.

Causes range from:

benign (IBS)
to
serious (IBD, cancer, malabsorption)

Your job is to:

✅ rule out red flags
✅ do simple first-line tests
✅ identify who needs colonoscopy
✅ avoid over-investigation

Not send every patient for a scope.

✅ First principle

Always ask:

Is this functional (IBS) or organic disease?

Because:

Organic → investigate
Functional → manage conservatively

The whole workup is about separating these two safely.

✅ Step 1 – Look for red flags FIRST (very important)

Before any tests, screen for danger signs.

If any present → investigate urgently.

🚨 Red flags

Weight loss
Rectal bleeding
Iron deficiency anaemia
Nocturnal diarrhoea
Fever
Severe pain
Family history CRC/IBD
Age >50 with new symptoms
Raised CRP

These suggest:

cancer
IBD
infection
serious pathology

👉 These patients usually need early colonoscopy

Do not label IBS.

✅ Step 2 – Characterise the diarrhoea (simple but high yield)

Basic history often gives the answer.

Ask:

Watery?

→ IBS, bile acid diarrhoea, endocrine, drugs

Bloody/mucus?

→ IBD, infection, cancer

Fatty/pale/floating?

→ malabsorption (coeliac, pancreatic)

Nocturnal?

→ organic disease (not IBS)

Post-meal urgency?

→ IBS or bile acid diarrhoea

Travel/antibiotics?

→ infection/C. diff

Often the story already points you in the right direction.

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

Do these before referring/scoping.

Bloods

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

These pick up:

anaemia
inflammation
coeliac
thyroid disease

Stool tests

Stool culture
C. difficile (if risk)
Faecal calprotectin

Calprotectin is very useful:

👉 low → IBS likely
👉 high → think IBD → scope

✅ Step 4 – Interpret results and decide next step

This is where juniors often get stuck.

🟢 Normal tests + no red flags

Likely:
👉 IBS or functional diarrhoea

No colonoscopy needed

Manage conservatively

🟡 Positive coeliac screen

👉 OGD with duodenal biopsy

🟡 High calprotectin / raised CRP

👉 colonoscopy (suspected IBD)

🟡 Iron deficiency anaemia

👉 colonoscopy ± OGD (cancer exclusion)

🟡 Steatorrhoea / weight loss

👉 think malabsorption
Check:

faecal elastase (pancreas)
imaging if needed

🟡 Persistent unexplained symptoms

👉 routine colonoscopy

✅ Step 5 – Common causes you’ll actually see

Focus on realistic NHS diagnoses.

Most common

IBS
Bile acid diarrhoea
Coeliac disease
IBD
Medications (metformin, laxatives, PPIs, antibiotics)

Less common but important

Pancreatic insufficiency
Microscopic colitis
Cancer
Thyroid disease

Don’t overthink rare causes early.

✅ Practical ward/clinic scenarios

Scenario 1

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

Scenario 2

Chronic diarrhoea + weight loss + high CRP
→ IBD likely
→ colonoscopy

Scenario 3

Iron deficiency anaemia only
→ scope for malignancy

Scenario 4

Bloating + anaemia + positive tTG
→ coeliac → OGD biopsy

Scenario 5

Older patient, watery diarrhoea, normal tests
→ consider microscopic colitis → colonoscopy with biopsies

✅ When to refer to gastro

Refer if:

red flags
positive calprotectin
iron deficiency anaemia
suspected IBD
malabsorption
persistent unexplained symptoms

Don’t refer typical IBS.

❌ Common junior mistakes

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

Keep it systematic.

✅ Simple ward algorithm

When you see chronic diarrhoea:

Red flags?
Bloods + stool tests
Calprotectin result
Organic vs functional
Scope only if indicated

That’s the whole approach.

✅ Take-home concept

Most chronic diarrhoea is IBS.
Your job is to rule out IBD, cancer, and coeliac safely.
Use simple tests first, then scope selectively.