Diarrhoea - adult's assessment
Exam Tips
- Use duration first: acute <14 days, persistent >=14 days, chronic >4 weeks; this framework is often mark-scoring.
- Differentiate osmotic vs secretory by fasting response: osmotic improves with fasting, secretory typically does not.
- Red flags for organic disease: nocturnal symptoms, rectal bleeding, weight loss, anaemia, fever, severe pain, age-related cancer risk.
- Always ask about recent antibiotics/hospital exposure to identify possible C. difficile early.
- In OSCE management, state contraindications to loperamide in bloody diarrhoea/high fever/suspected severe colitis.
- Structured stool history (frequency, volume, blood, mucus, steatorrhoea, urgency, nocturnal pattern, travel, drugs, diet) helps separate functional from inflammatory/malabsorptive causes.
Definition
Diarrhoea in adults is the passage of at least three loose or watery stools in 24 hours, or stool frequency/consistency that is clearly above that person’s normal baseline. Clinically it is classified by duration into acute (<14 days), persistent (14 days or more), and chronic (>4 weeks), which helps narrow causes and urgency of investigation.
Pathophysiology
Diarrhoea results from disordered intestinal water and electrolyte handling, usually through one or more mechanisms: osmotic load, secretory drive, mucosal inflammation, or altered motility. Osmotic diarrhoea occurs when poorly absorbed solutes (for example sorbitol, magnesium salts, lactose in intolerance, broader malabsorption) retain water in the lumen and typically improves with fasting. Secretory diarrhoea is driven by active chloride/water secretion or reduced absorption (for example enterotoxin-producing infections, bile acids in colon after ileal disease/resection, drug effects) and often persists despite fasting. Inflammatory diarrhoea reflects epithelial injury and cytokine-mediated permeability changes (for example IBD or invasive infection), causing reduced absorption plus exudation of blood/protein; nocturnal symptoms and systemic upset are more likely. Motility-predominant states shorten transit and reduce contact time for absorption (for example hyperthyroidism, diabetic autonomic dysfunction, IBS-pattern disease). See Figure: intestinal absorption-secretion balance and diarrhoea mechanisms in a core GI physiology text.
Risk Factors
- Recent infectious exposure (household/outbreak setting, contaminated food or water, travel)
- Recent antibiotic use (especially with healthcare exposure), raising suspicion for Clostridioides difficile
- Older age, immunocompromise, and recent hospitalization
- Drugs that can cause diarrhoea (for example metformin, PPIs, SSRIs, NSAIDs, magnesium-containing antacids, laxatives, ARBs, chemotherapy)
- Known GI disease or surgery (Crohn’s disease, ileal resection, coeliac disease, pancreatic insufficiency)
- Dietary triggers (high FODMAP intake, excess caffeine/alcohol, artificial sweeteners such as sorbitol)
Clinical Features
Symptoms
- Frequent loose/watery stools, urgency, possible incontinence
- Abdominal cramps, bloating, nausea/vomiting
- Fever or constitutional upset in infective/inflammatory causes
- Blood or mucus in stool suggests invasive infection, IBD, ischaemia, or malignancy
- Nocturnal diarrhoea (more suggestive of organic pathology than functional IBS)
- Weight loss, fatigue, steatorrhoea, or prolonged symptoms suggesting malabsorption/chronic disease
Signs
- Dehydration: dry mucosa, reduced skin turgor, postural dizziness/hypotension, tachycardia, oliguria
- Fever and abdominal tenderness; localized peritonism may indicate alternative acute abdomen
- Signs of severe illness/sepsis: hypotension, confusion, poor peripheral perfusion
- Pallor or weight loss in chronic disease (for example iron deficiency from colorectal pathology or coeliac disease)
- Abdominal or rectal mass, or visible rectal bleeding, increasing concern for colorectal cancer
- Features of systemic disease (for example thyroid overactivity signs, diabetic autonomic features)
Investigations
Management
Lifestyle Modifications
- Early oral rehydration and salt replacement; small frequent fluids and temporary avoidance of dehydration-promoting intake (alcohol/caffeine excess)
- Review and remove potential drug/diet triggers where safe (for example sorbitol-containing products, excess FODMAP load)
- Infection-control advice for likely gastroenteritis: strict hand hygiene and avoidance of food preparation for others while symptomatic
- Safety-net for urgent review: worsening dehydration, persistent fever, blood in stool, severe abdominal pain, reduced urine output, or symptoms >14 days
Pharmacological Treatment
Oral rehydration therapy
- Oral rehydration salts (for example Dioralyte): 1 sachet dissolved in 200 mL water after each loose stool
First-line in most adults with acute diarrhoea. Monitor frail adults and those with renal/cardiac comorbidity for fluid/electrolyte balance.
Antimotility
- Loperamide: 4 mg initially, then 2 mg after each loose stool (usual max 16 mg/day in adults)
Useful for short-term symptomatic control in uncomplicated, non-bloody diarrhoea. Avoid/caution in suspected acute dysentery, high fever, severe colitis, or suspected C. difficile because of toxic megacolon risk.
Targeted anti-infective therapy
- Oral vancomycin 125 mg four times daily for 10 days for confirmed non-severe C. difficile infection
- Fidaxomicin 200 mg twice daily for 10 days as an alternative first-line option in C. difficile
Do not give empiric antibiotics routinely for self-limiting community diarrhoea. Reserve treatment for confirmed/suspected specific pathogens, severe disease, or high-risk patients; follow local microbiology guidance.
Surgical / Interventional
- No routine surgical treatment for uncomplicated diarrhoea
- Urgent surgical review if concern for complications/alternative diagnoses such as bowel ischaemia, perforation, toxic megacolon, or acute abdomen
Complications
- Dehydration with acute kidney injury and electrolyte disturbance
- Sepsis in severe invasive infection
- Malabsorption, weight loss, micronutrient deficiency in chronic diarrhoea
- Quality-of-life impairment (social restriction, anxiety about toilet access)
- Condition-specific complications (for example IBD flare complications, colorectal cancer delay)
Prognosis
Most acute infectious episodes are self-limiting with supportive care, but prognosis worsens with severe dehydration, frailty, immunosuppression, or delayed recognition of serious organic pathology. Persistent or chronic diarrhoea has a variable course and depends on identifying and treating the underlying cause (for example coeliac disease, microscopic colitis, bile acid diarrhoea, IBD, or malignancy).
Sources & References
âś…NICE Guidelines(1)
- Diarrhoea - adult's assessment[overview]