Gastroenterology · Full case
Diarrhoea
Diarrhoea · Clinical Reasoning Framework v2
GP & SCA · NICE CKS · Acute (infective) vs chronic · Dehydration · Bloody diarrhoea · Coeliac/IBD/IBS · FIT & NG12 · Public-health
Acute vs chronic is the forkAcute diarrhoea (<2 weeks) is usually infective/self-limiting — focus on hydration, red flags and public health. Chronic diarrhoea (>4 weeks) needs a structured work-up for coeliac, IBD, IBS, colorectal cancer, malabsorption and other causes
Hydration is the priorityIn acute diarrhoea the immediate task is assessing and correcting dehydration — oral rehydration first-line; watch the very young, the elderly and the frail, who decompensate fastest. Most acute infective diarrhoea needs no antibiotics or stool tests
Bloody diarrhoea changes everythingBlood in the stool with diarrhoea raises invasive infection (Campylobacter, Shigella, E. coli O157, amoebiasis), inflammatory bowel disease, and ischaemic colitis. It warrants stool testing, caution with anti-motility/antibiotics (E. coli O157 → HUS risk), and a lower threshold to refer
Don't miss the cancerA persistent change in bowel habit to looser/more frequent stools (especially 50+, or with rectal bleeding, weight loss, iron-deficiency anaemia, an abdominal/rectal mass) needs FIT and the NICE NG12 colorectal pathway — diarrhoea can be the presenting symptom of bowel cancer
FIT + faecal calprotectinFIT (≥10 µg Hb/g) flags possible colorectal cancer and is now used in symptomatic patients to guide urgent referral; faecal calprotectin distinguishes inflammatory (IBD) from non-inflammatory (IBS) bowel disease in younger adults without alarm features
Always test for coeliacTest for coeliac disease (anti-tTG IgA + total IgA) in anyone with persistent/unexplained diarrhoea or IBS-type symptoms — the patient must be eating gluten for the test to be valid. It is commonly missed for years
C. difficile after antibioticsDiarrhoea during/after antibiotics (or PPIs), especially in the elderly or recently hospitalised, raises Clostridioides difficile — send stool, stop the precipitant where possible, treat per guidance, and isolate. It can be severe
Public health & the exclusionsNotify suspected infectious bloody diarrhoea/food-poisoning; advise on hygiene and 48-hour exclusion after symptoms settle for food handlers, healthcare/social-care staff and children — essential in outbreaks and high-risk occupations
📋 Clinical Stem — Diarrhoea
A 58-year-old man with 6 weeks of looser, more frequent stools, attributing it to a "bug", who on questioning has also lost weight and seen some blood
Trevor Hughes, 58, comes in because his bowels "still aren't right" after what he assumed was a stomach bug. For about 6 weeks he has been opening his bowels 3–4 times a day with looser stools, sometimes urgently. On gentle questioning he has lost about 5kg, noticed some blood mixed in once or twice, and feels more tired than usual. There is no foreign travel, no recent antibiotics, and no obvious unwell contacts. His father had bowel cancer in his 60s. He is otherwise well, eats a normal diet including gluten, and hoped for "something to settle it down".
This stem tests the ability to: separate acute from chronic diarrhoea and recognise that a persistent (≥4 week) change in bowel habit in a 58-year-old with weight loss, rectal bleeding, fatigue (?iron-deficiency anaemia) and a family history is a colorectal-cancer red-flag presentation requiring FIT and the NICE NG12 pathway — not a "bug"; to structure the chronic-diarrhoea work-up (bloods including FBC/ferritin/coeliac serology/CRP, FIT, faecal calprotectin where appropriate, stool tests if indicated); to consider IBD, coeliac, IBS and other causes; to safety-net and avoid false reassurance; and to handle the patient's wish for a quick fix while explaining why investigation is needed. The SCA challenge is converting a "settle my stomach" request into appropriate cancer-pathway investigation without causing undue alarm — and not anchoring on the patient's "bug" explanation.
Scenario A — Chronic change + red flags (this stem) ≥4 weeks looser stools, weight loss, rectal bleeding, fatigue, family history, age 58. FIT + bloods (FBC/ferritin/coeliac/CRP) + NG12 colorectal referral; examine incl. PR; safety-net.
Scenario B — Acute infective diarrhoea <2 weeks, self-limiting; assess dehydration, oral rehydration, hygiene/exclusion advice, no routine antibiotics/stool tests; stool test if bloody/systemic/recent travel/immunocompromised/public-health.
Scenario C — IBD Younger adult, chronic/bloody diarrhoea, nocturnal symptoms, weight loss, raised calprotectin/CRP. Refer gastroenterology; don't mislabel as IBS.
Scenario D — Coeliac / malabsorption Chronic diarrhoea, bloating, weight loss, anaemia; positive anti-tTG (on gluten). Confirm + gastroenterology; consider other malabsorption (pancreatic, bile-acid).
Scenario E — IBS / functional Younger, no alarm features, normal FIT/calprotectin/coeliac; positive symptom pattern. Positive diagnosis + management — a diagnosis of inclusion after excluding red flags, not pure exclusion.
Key variables to adapt for Acute vs chronic; dehydration/frailty; bloody diarrhoea; cancer red flags + FIT/NG12; IBD vs IBS (calprotectin); coeliac (on gluten); C. difficile (antibiotics/PPI); travel/immunocompromise; medication (laxatives, metformin, PPI, colchicine); overflow in constipation; public-health/exclusion.
Steps:
1
Step 1
History — Acute vs Chronic · Stool · Red Flags · Causes · ICE
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The first fork is duration: acute (<2 weeks, usually infective) versus chronic (>4 weeks, needs a work-up). Then characterise the stool, screen hard for the red flags (blood, weight loss, anaemia, age, family history), and identify treatable causes. Trevor frames it as a lingering "bug"; the danger is accepting that label when the duration, weight loss, blood and family history shout colorectal cancer.
🎓 SCA framing — don't inherit the "bug" label
"Six weeks is longer than a bug usually lasts, and a couple of things you've mentioned — the weight loss and the blood — mean I'd be doing you a disservice if I just gave you something to settle it. Let me ask a bit more and check things properly."
Trevor wants a quick fix and has explained it away. The skill is to gently reframe the duration and red flags as reasons to investigate — without frightening him — rather than anchoring on his diagnosis.
1A — Duration, stool, red flags and causes
1B — Red flags
🚨
Red Flags — when diarrhoea is not "just a bug"
| Red flag | Why it matters | Action |
|---|---|---|
| Persistent change in bowel habit (≥4–6 weeks) to looser/more frequent stools, esp. 50+, with rectal bleeding / weight loss / iron-deficiency anaemia / abdominal or rectal mass | Colorectal cancer — diarrhoea can be the presenting symptom. | FIT + NICE NG12 colorectal pathway; FBC/ferritin; PR/abdominal exam |
| Bloody diarrhoea | Invasive infection (incl. E. coli O157 → HUS), IBD, ischaemic colitis; anti-motility/antibiotics may be harmful. | Stool tests; avoid anti-motility/empirical antibiotics in possible O157; assess for IBD; refer if needed |
| Dehydration / shock — especially infants, elderly, frail, immunocompromised | Rapid decompensation; electrolyte disturbance; AKI. | Rehydrate; admit if severe / unable to maintain hydration |
| C. difficile (diarrhoea during/after antibiotics or PPI, elderly, recent hospital) | Can cause severe colitis/toxic megacolon. | Stool for C. diff; stop precipitant; treat per guidance; isolate; assess severity |
| Features of IBD — chronic/bloody diarrhoea, nocturnal symptoms, weight loss, raised CRP/calprotectin, mouth/joint/eye/skin signs | Needs specialist diagnosis/treatment; flares can be serious. | Calprotectin/CRP; gastroenterology referral; don't mislabel as IBS |
| Severe abdominal pain / peritonism / systemic sepsis | Surgical abdomen, ischaemic colitis, severe colitis. | Same-day surgical/medical assessment |
1C — ICE
💭 Ideas
"What do you think has been causing it — you mentioned a bug?"
Trevor has explained it away as a lingering bug. Surfacing this lets you gently challenge the timeline and explain why the duration and the blood/weight loss change the approach — recruiting him into investigation rather than contradicting him bluntly.
😟 Concerns
"Is there anything you've been worried it might be — your dad's history, perhaps?"
He may be privately frightened (the family history, the blood) or genuinely unworried. Naming it lets you pitch the cancer-pathway investigation as sensible thoroughness — neither dismissive nor alarmist.
🎯 Expectations
"You were hoping for something to settle it — can I explain why I want to check a few things first?"
He expects symptomatic treatment. Naming this lets you explain why tests come first, set out the FIT/bloods/possible referral, and agree a plan — so he leaves understanding the reasoning rather than feeling fobbed off into tests.
1D — Psychosocial context
🔎 Reframing the bug
Challenge the timeline gently but clearly.
"A bug rarely lasts six weeks, and the weight loss and blood aren't part of a simple bug — so rather than just settling it, I want to find out what's actually going on."🧫 The embarrassing questions
Normalise asking about blood and bowels.
"I'm going to ask some questions people find awkward, and I'll need to examine your tummy and back passage — it's routine and important, and it's the quickest way to keep you safe."⚖️ Thorough, not alarming
Pitch the cancer-pathway tests proportionately.
"Most of the time these tests are reassuring. I'd rather check properly now than miss something — that's just being thorough given your age and what you've told me."👨👩👦 The family history
Acknowledge his father's cancer honestly.
"With your dad having had bowel cancer, I know this might be on your mind — that's another reason to do the right checks now and not just paper over it."🎓 SCA Checkpoint — Step 1TasksRelating to OthersGlobal Skills
Key phrases that score
"Six weeks is too long for a bug." — refuses to inherit the label.
"Any weight loss, blood, or family history of bowel cancer?" — the red-flag screen.
"I'd like to do a stool test called FIT and some bloods, and examine you including your back passage." — the right work-up.
Deductions
- Accepting "it's a bug" and giving symptomatic treatment only
- Not screening red flags / not arranging FIT + bloods
- Not asking about coeliac/medication/infective causes
- Not examining (abdomen ± PR)
🔴 Red
Anchors on "bug"; no red-flag screen; no FIT/bloods; no PR; reassures falsely
🟠 Amber
Recognises chronic; some bloods/FIT; red flags partly screened; coeliac/PR omitted; ICE partial
🟢 Green
Acute vs chronic clarified; red flags screened; FIT + FBC/ferritin/coeliac/CRP; considers IBD/coeliac/IBS/infection; examines incl. PR; NG12 referral; ICE all three; safety-net
2
Step 2
Triage — Emergency · Urgent (Cancer/IBD/C. diff) · Routine
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Triage separates the dehydrated/septic/severely-bleeding patient (same day), the cancer/IBD/C. difficile group (urgent investigation/referral), and routine acute or functional diarrhoea. Trevor sits in the urgent cancer-pathway lane.
🔴 Emergency
Same day / 999
Immediate action- Severe dehydration / shockEspecially frail/elderly/infant → admit
- Severe colitis / peritonism / sepsisSame-day assessment
- Significant GI bleedingUrgent admission
🟠 Urgent
Days–2 weeks
Investigate / refer- Cancer red flagsFIT + NG12 colorectal referral; bloods
- Suspected IBDCalprotectin/CRP; gastroenterology
- C. difficile / significant infectionStool tests; treat; public health
🟢 Routine
Primary care
Manage / work-up- Acute infective (well, hydrated)Rehydration, hygiene/exclusion, no routine antibiotics
- Chronic, no red flagsBloods, coeliac, calprotectin; consider IBS
- Drug/dietary causeReview medication/diet
🎓 SCA Checkpoint — Step 2Tasks
Triage rationale
"Because of your age, the weight loss and the blood, this goes down a fast-track bowel pathway — a stool test and bloods now, and very likely a camera test — rather than being treated as a simple tummy upset."
Deductions
- Treating a red-flag presentation as routine
- Missing dehydration in the vulnerable / C. diff after antibiotics
3
Step 3
Examination — Hydration · Abdomen · PR · Systemic/Nutritional Signs
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Examination assesses hydration/haemodynamics, the abdomen (mass, tenderness), the rectum (mass, blood — a PR is part of the work-up of a change in bowel habit), and systemic/nutritional signs of chronic disease.
🎓 SCA Checkpoint — Step 3TasksGlobal Skills
Narration that scores
"I'll check for dehydration, examine your tummy for any lump or tenderness, and — with your consent and a chaperone — examine your back passage, which is an important part of checking this properly."
Deductions
- Omitting PR / abdominal exam in a change of bowel habit
- Not assessing hydration in acute/vulnerable patients
4
Step 4
Investigations — FIT · Bloods · Coeliac · Calprotectin · Stool Tests
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Acute infective diarrhoea usually needs no tests; chronic diarrhoea needs a structured panel — bloods, coeliac serology, FIT for the cancer pathway, faecal calprotectin to separate IBD from IBS, and targeted stool tests.
🎓 SCA Checkpoint — Step 4Tasks
Key reasoning
"I'll do a FIT stool test and bloods including iron levels and a coeliac test, and examine you — that combination tells me whether this needs an urgent bowel-cancer referral or points to something like coeliac or inflammation."
Deductions
- Not doing FIT/bloods in a red-flag presentation
- Forgetting coeliac serology; ordering calprotectin when alarm features mandate cancer referral anyway
5
Step 5
Diagnosis — Acute Infective · Cancer · IBD · Coeliac · IBS · Other
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Integrate duration, stool features, red flags and tests to name the cause — and remember IBS is a positive diagnosis made after excluding red flags, not a label of convenience.
🚩 IBS is a positive diagnosis — and Trevor isn't IBS
The classic error is to reach for "IBS" or "a bug" in a patient with alarm features. IBS is diagnosed positively (typical symptoms, normal investigations, no red flags), usually in younger patients. For Trevor — 58, ≥4 weeks of looser stools, weight loss, rectal bleeding, fatigue and a family history — the formulation is a colorectal-cancer red-flag presentation requiring FIT and the NG12 pathway, with IBD and coeliac also in view. The discipline is to exclude the serious before comforting with the benign.
🎓 SCA Checkpoint — Step 5Tasks
Explaining it plainly
"Because this has gone on for weeks with some weight loss and blood, I don't want to just call it a bug or IBS. I'd like to investigate properly and, given your age and symptoms, refer you on the fast bowel pathway — most often it's reassuring, but it's the right thing to do."
Deductions
- Diagnosing IBS/"bug" in the presence of alarm features
- Not naming the need for cancer-pathway referral
6
Step 6
Referral — Emergency · 2WW Colorectal · Gastroenterology · Public Health
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Referral follows the differential: emergencies admitted; the cancer pathway (FIT-guided NG12) for red-flag change in bowel habit; gastroenterology for IBD/coeliac/refractory chronic diarrhoea; and public-health notification for relevant infections.
🎓 SCA Checkpoint — Step 6Tasks
Stating the threshold
"Given your age, the change lasting weeks, the weight loss and the blood, the guidance is to refer you urgently on the bowel-cancer pathway and to do a FIT test — so you're seen quickly and we get a clear answer."
Deductions
- Not referring red-flag change in bowel habit (NG12)
- Not notifying/advising exclusion for relevant infections
7
Step 7
Management — Hydration · Treat the Cause · Anti-motility Caution · Public Health · Safety-Net
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Management depends on the cause: rehydration and supportive care for acute infective diarrhoea (with careful anti-motility and antibiotic use), cause-specific treatment for chronic disease, public-health/exclusion advice, and — for a red-flag presentation like Trevor's — investigation/referral with a clear safety-net rather than symptomatic treatment alone.
7A — By setting
🎓 SCA Checkpoint — Step 7TasksRelating to OthersGlobal Skills
A plan that scores
"Here's the plan: a FIT test and bloods today, an urgent bowel-pathway referral, and I'll examine you now. I won't just give you something to plug it up, because that could hide what's going on. Come back sooner if you bleed heavily, get severe pain, or can't keep fluids down — and we'll go through the results together."
Deductions
- Prescribing loperamide to a red-flag/bloody-diarrhoea patient instead of investigating
- No public-health/exclusion advice in infective cases
- No safety-net or result follow-up
Diarrhoea — SCA Consultation Scorecard
Acute vs chronic · red flags + FIT/NG12 · coeliac/IBD/IBS · hydration · public health
0/ 33 pts
Global Skills
Structure, language, responsiveness
0/7
Tasks
Clinical reasoning, diagnosis, management
0/15
Relating to Others
Communication, rapport, shared decisions
0/11
RAG Self-Assessment
🔴 Red
Anchors on "bug"/IBS; no red-flag screen/FIT; no PR; loperamide for bloody diarrhoea; false reassurance
🟠 Amber
Recognises chronic; some bloods/FIT; coeliac/PR or public-health partly addressed; ICE partial
🟢 Green
Acute vs chronic; red flags → FIT + NG12; FBC/ferritin/coeliac/CRP; PR; anti-motility caution; public health; avoids anchoring; ICE all three; safety-net
Complete the checklist to see your score and feedback
"Doc, my stomach's still not right after what I thought was a bug — I'm going to the toilet a lot, loose, for about six weeks now. Can you give me something to settle it down?"
Who you are
Trevor Hughes, 58. About 6 weeks of looser, more frequent stools (3–4 times a day), sometimes urgent. You assumed it was a stomach bug that's hung around. If asked, you've lost about 5kg without trying, seen some blood mixed in once or twice, and feel more tired than usual. No foreign travel, no recent antibiotics, no obviously unwell contacts. Your father had bowel cancer in his 60s. You eat normally (including bread/pasta). You came hoping for something to settle your stomach and didn't really want a fuss.
Hidden concerns (reveal if explored)
Cancer fear (main, often unspoken): your dad's bowel cancer is at the back of your mind; you've half-avoided thinking about the blood. If the doctor is calm and thorough, you're relieved to be taken seriously.
Embarrassment: you're a bit reluctant to talk about blood/the back passage but will if the doctor is matter-of-fact.
Wanting a quick fix: you'd prefer a tablet, but accept investigation when the reasoning is explained.
Clinical details if asked
- ~6 weeks looser/more frequent stools, urgency; blood mixed in once or twice; ~5kg unintentional weight loss; increased fatigue
- No travel, no recent antibiotics/PPI, no clear unwell contacts, no fever
- Father had bowel cancer in his 60s; you eat gluten normally
- No severe pain; tolerating fluids; passing urine normally (not dehydrated)
- On examination: happy to consent to abdominal and PR exam with a chaperone
Reactions at key moments
- On "six weeks is too long for a bug": pauses, takes it on board.
- On the FIT/bloods/referral: slightly anxious but reassured by the calm, clear explanation.
- On the family history being mentioned: admits it's been worrying you.
- On PR exam: a bit embarrassed but consents when it's explained.
- Challenge line: "Can't you just give me something to stop it? I'm sure it's nothing serious."
"Honestly doc, can't you just give me something to bung it up? I'm sure it's just a bug that's hanging around — I don't really want a load of tests."
Resolution: Trevor is well served if the GP: (1) refuses to inherit the "bug" label, recognising 6 weeks of changed bowel habit with weight loss, rectal bleeding, fatigue and a family history as a colorectal-cancer red-flag presentation; (2) screens the red flags, examines (abdomen + PR), and arranges FIT + bloods (FBC/ferritin/coeliac/CRP); (3) refers on the NG12 colorectal pathway and avoids simply prescribing loperamide; (4) explains the reasoning calmly — thorough, not alarmist — and acknowledges the family-history worry; (5) safety-nets and arranges result follow-up. He is poorly served if given an anti-motility and sent away, or falsely reassured it's "just a bug".
Clinic Quick Reference
Diarrhoea — Clinical Decision Framework
Acute vs chronic · red flags + FIT/NG12 · coeliac/IBD/IBS
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🚦 1 — Acute vs chronic
Acute (<2 wk)
Usually infective/self-limiting. Assess dehydration; oral rehydration; no routine antibiotics/stool tests; stool test if bloody/systemic/travel/immunocompromised/public-health. Anti-motility caution (not in bloody/O157/C. diff).
Chronic (>4 wk)
Work-up: FBC/ferritin, CRP, coeliac serology (on gluten), TFTs; FIT; faecal calprotectin (IBD vs IBS). Examine incl. PR.
🚩 2 — Red flags · refer
Persistent change in bowel habit, 50+, rectal bleeding, weight loss, iron-deficiency anaemia, mass → FIT + NICE NG12 colorectal pathway. IBD (bloody/nocturnal, raised calprotectin/CRP) → gastroenterology. Coeliac → confirm + dietitian. IBS = positive diagnosis after excluding red flags. C. diff after antibiotics/PPI → stool + treat. Public-health notification/exclusion for relevant infections.
SCA Quick Reference
Diarrhoea — Consultation Playbook
Acute vs chronic · don't inherit "bug"/IBS · FIT + NG12 · safety-net
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🎯 The three pivots that pass this case
1 · Duration first
≥4 weeks of changed bowel habit isn't a "bug" — it's a chronic presentation needing a work-up.
2 · Red flags → FIT/NG12
Age 50+, bleeding, weight loss, IDA, family history → FIT + colorectal pathway + bloods + PR. Test coeliac.
3 · Don't just plug it
Avoid anti-motility/empirical antibiotics in bloody diarrhoea/O157; investigate, safety-net, follow up results.
⛔ Don't inherit the patient's "bug"/IBS label with alarm features present · Don't skip FIT, bloods, coeliac serology or PR in a change of bowel habit · Don't give loperamide/empirical antibiotics in bloody diarrhoea or possible E. coli O157 · Don't forget hydration in the vulnerable and public-health/exclusion advice · IBS is a positive diagnosis after red flags are excluded