Differential diagnosis of diarrhoea and constipation

1. Big picture

Diarrhoea and constipation are symptoms, not diagnoses. In the exam, the safest approach is:

First decide whether the patient is acutely ill or chronically symptomatic → identify red flags → classify the stool pattern → choose targeted tests.

The most important clinical split:

Always ask: Is there blood, fever, weight loss, dehydration, severe pain, anemia, nocturnal symptoms, or new onset after age 50? These are red flags.

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