Reasoning GP · Algorithm · 1-page summary
Acute diarrhoea in adults
For: adults with diarrhoea for less than 14 days in primary care. Not for: children (children's pathway, NICE CG84 under 5s); diarrhoea for 4 weeks or more (use the chronic diarrhoea algorithm).
Core rule: judge hydration, sepsis and the abdomen before the stool. Bloody diarrhoea with severe pain is STEC until excluded — no loperamide, no antibiotic without advice.
0Stop — call 999 now
- Shock or high-risk sepsis: hypotension, new confusion, mottled skin, RR ≥25, HR >130 → 999
- Peritonitis or acute abdomen with shock → 999
- Diabetes: drowsy or Kussmaul breathing (DKA, including euglycaemic DKA on an SGLT2 inhibitor) → 999
- Steroid-dependent, vomiting and unwell → IM hydrocortisone and 999
1Triage — hydration decides the setting
| Finding | Where |
|---|---|
| Drinking, passing urine, well | Home: fluids, self-care, safety-net |
| Older, frail, pregnant, comorbid | ORS, U&E, review within 24 h; lower threshold to admit |
| Severe dehydration, can't keep fluids | Same-day assessment ± IV fluids |
| Blood in stool | Stool "suspected STEC", CRP, U&E; severe pain → Same-day |
2Screen
- HUS: less urine, pallor, bruising after bloody diarrhoea → Same-day; notify HPT
- Severe C. difficile: recent antibiotics + fever, distension, AKI → Same-day
- Acute abdomen or older patient with pain out of proportion → Same-day surgical
- Fever after malaria-area travel → malaria films Same-day
- Neutropenic risk (chemotherapy within 6 weeks + fever or unwell) → Immediate acute oncology hotline / 999
- Acute severe colitis (6 or more bloody stools a day + systemic upset) → Same-day
3Assess
☐ Obs, postural BP, urine output, mental state ☐ Abdomen ± PR (overflow) ☐ Glucose ± ketones in diabetes ☐ Drug review (metformin, laxatives, PPI, antibiotics in 12 weeks) ☐ Travel, food, contacts, occupation
Stool if blood, systemic, immunocompromised, recent antibiotics/hospital (C. difficile), beyond 7 days, travel, outbreak or risk-group job. Not for short, well, non-bloody illness.
4Classify
- Viral — vomiting, outbreaks, settles in 1–3 days → fluids.
- Bacterial — fever, blood, poultry or contacts → stool; antibiotics only on advice.
- C. difficile — recent antibiotics, PPI, care home → stop trigger, stool, vancomycin if confirmed.
- Drug — metformin, laxatives, magnesium → change the drug.
- IBD, ischaemic colitis, overflow — bloody beyond 7 days, vascular patient, faecal loading.
- Uncertain — review in 7 days; persisting → stool and the chronic pathway.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Fluids; ORS 200–400 mL after each loose stool if higher risk. Eat normally.
- Loperamide 4 mg then 2 mg per loose stool, max 16 mg in 24 h — not with blood, fever, C. difficile or STEC.
- Sick-day rules: pause metformin, SGLT2i, ACEi/ARB, diuretics, NSAIDs; never stop insulin; double steroid dose.
- Exclusion 48 hours after last episode; notify suspected food poisoning to HPT.
6Refer routinely
- Suspected IBD → gastroenterology Urgent; persisting with negative stool → chronic diarrhoea pathway.
- Persistent change in bowel habit, rectal bleeding, IDA → FIT and NG12 colorectal pathway.
7Never reassure by
- Normal skin turgor in an older adult.
- Few stools in an ill patient on antibiotics (C. difficile ileus).
- A normal glucose in a vomiting patient on an SGLT2 inhibitor.
- "Gastroenteritis" with pain out of proportion in an older patient.
- Diarrhoea in a frail, constipated patient (overflow).
- No fever in a returning traveller who felt hot yesterday.
8Safety-net — say it, then document it
999 “Call 999 if you collapse, become confused or drowsy, or pass or vomit a lot of blood.” Same-day “Contact us today if you can't keep fluids down, pass very little urine, feel dizzy on standing, see blood, get worse tummy pain or a high fever — or, after bloody diarrhoea, pass less urine, look pale or bruise.” Not settling in 7 days → review and stool.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Hydration and obs documented
Drug review and sick-day advice given
Stool sent if indicated; HPT notified if needed
Exclusion, review date and safety-net given
Summary of the full Reasoning GP acute diarrhoea algorithm, which holds the detail, examination, investigations and evidence. Sources: UKHSA, NICE NG199, NG253, NG12, CKS Gastroenteritis; product SPCs. Clinical reference — follow local pathways; doses: NICE/SPC, BNF, local formulary.