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Surgical sieve
💩 Diarrhoea
Three questions: is there blood, have they had antibiotics, and did this start IN hospital? Each one takes you somewhere "it is just gastroenteritis" does not.
| C. difficile colitis Must exclude | Diarrhoea during or up to 12 weeks after antibiotics — classically the 4 Cs, but any antibiotic can do it. Rising white count, low albumin, and pain out of proportion suggest severe disease.Isolate and send a sample on suspicion, not on confirmation. Stop the precipitating antibiotic where possible. NEVER give loperamide. |
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| Neutropenic sepsis Must exclude | Diarrhoea within 6 weeks of chemotherapy. The diarrhoea may be the only symptom, and the fever may be absent.FBC and antibiotics within one hour of suspicion. Do not wait for the count. |
| Mesenteric ischaemia Must exclude | Pain out of all proportion to the examination, with diarrhoea that may be bloody, in an arteriopath or someone in AF. A rising lactate with a soft abdomen.CT angiogram and surgeons. The window is hours, and the examination is reassuring right up until it is not. |
| Lower GI bleed Must exclude | Frank blood or clots rather than blood-streaked stool. Brisk upper GI bleeding can present as maroon stool with a normal-looking upper GI history.Resuscitate first. A raised urea with a normal creatinine points upward, not downward. |
| Toxic megacolon Must exclude | Known or new colitis with systemic toxicity — fever, tachycardia, distension — and a transverse colon over 6cm on plain film. Bloody diarrhoea that suddenly SETTLES can mean the colon has stopped working, not improved.Surgeons and gastroenterology together. Stop antimotility agents and opioids. |
| Inflammatory bowel disease Time-sensitive | Bloody diarrhoea with urgency, tenesmus and nocturnal stools, often with weight loss or extraintestinal features. Nocturnal diarrhoea is not functional.Truelove and Witts for severity in ulcerative colitis. Stool culture to exclude infection alongside, not instead. |
| Overflow diarrhoea Time-sensitive | Frequent small liquid stools in a constipated patient, often opioid-related, often in the frail. The history sounds like diarrhoea and the abdomen is loaded.Consider a digital rectal examination where faecal impaction or overflow is suspected, before treating this as diarrhoea. Loperamide here makes it worse — this needs disimpaction, not slowing down. |
| Gastroenteritis Common | Vomiting then watery diarrhoea, others affected, self-limiting within 48 to 72 hours. Norovirus closes wards.Rehydration and isolation. Send a sample if bloody, if recent travel, if immunosuppressed, or if it persists. |
| Drug toxicity or withdrawal Time-sensitive | Laxatives given and not stopped, magnesium, metformin, PPIs, colchicine, chemotherapy, and enteral feed. Also opioid WITHDRAWAL.Read the chart before sending three stool samples. A stopped laxative is a faster fix than a microbiology result. |
| Enteral feed intolerance Common | Diarrhoea in a patient on NG or PEG feed, often rate-related or from the sorbitol in co-administered liquid medicines.Review the feed rate and the liquid medications with dietetics and pharmacy before reaching for a stool sample. |
| Sepsis (any source) Time-sensitive | Diarrhoea can be a non-specific feature of sepsis from any source, particularly in the elderly and in intra-abdominal infection.Look for the source elsewhere if the story does not fit the gut. |
| Hyperthyroidism Consider | Frequent loose stools with weight loss, tremor, heat intolerance and tachycardia or new AF.TFTs. Diarrhoea with an unexplained tachycardia is worth a thyroid thought. |
| Malabsorption Consider | Steatorrhoea — pale, greasy, hard to flush — with weight loss. Coeliac disease, pancreatic insufficiency, or bile acid malabsorption after cholecystectomy.A subacute story, not an on-call one. Coeliac serology and faecal elastase, with outpatient follow-up. |
| Malignancy Consider | A persistent change in bowel habit with weight loss, iron deficiency anaemia or rectal bleeding, particularly over 50.Not an overnight diagnosis, but it is an overnight REFERRAL — make sure someone owns the follow-up. |
| Irritable bowel syndrome Consider | Long history, relation to stress and food, no weight loss, no blood, and no nocturnal symptoms.A positive diagnosis in a young patient with no red flags — not a label to hang on a new presentation in an older one. |
15 differentials · 6 open a full pathway in the app.