Diarrhoea in Adults

Differential Diagnosis

Common Diagnoses

Occasional Diagnoses

Rare Diagnoses

  • HIV Infection
  • Appendicitis
  • Laxative Misuse
  • Thyrotoxicosis
  • Malabsorption, Various Causes
  • Allergy
  • Ovarian Cancer

Ready Reckoner

Key distinguishing features of the most common diagnoses

Vomiting TooPossiblePossibleNoPossibleNo
Chronic or RecurrentNoNoYesPossibleYes
Constant Severe PainNoNoNoYesNo
Marked Abdominal TendernessNoNoNoYesNo
Blood in StoolPossiblePossibleNoPossibleNo

Possible Investigations

Likely:If persistent, stool specimen, FBC, ESR/CRP, TFT, anti-endomysial and anti-gliadin antibodies, faecal calprotectin.

Possible:Urinalysis, LFT, FIT, hospital-based lower GI investigations, CA-125.

Small Print:HIV test, tests for malabsorption.

  • One stool sample is sufficient in acute diarrhoea of more than a week to look for common infections.
  • Series of three daily stool samples necessary to look for ova, cysts and parasites in chronic diarrhoea.
  • FBC: Hb may be reduced and ESR/CRP elevated in IBD and malignancy; iron deficiency anaemia in neoplasia, coeliac disease; diverticulitis – check ferritin, B12 and folate too; WCC raised in IBD and infection.
  • TFT: Will reveal thyrotoxicosis.
  • Anti-endomysial and anti-gliadin antibodies: Suggest coeliac disease if positive.
  • Faecal calprotectin: Helps rule out inflammatory bowel disease.
  • LFT: May suggest secondaries or alcoholism.
  • FIT: A useful colorectal cancer ‘rule out’ test in patients at low risk. Also commonly required now when arranging a two-week referral to help secondary care stratify urgency of investigation.
  • Urinalysis: Specific gravity high in dehydration.
  • Hospital-based lower GI investigations: Will confirm diagnosis of malignancy, diverticulosis, carcinoma and IBD.
  • CA-125: To help exclude ovarian cancer – especially in women aged 50 or more.
  • HIV test: For HIV infection.
  • Tests for malabsorption: Such as stool fat analysis, lactose tolerance test, small intestinal biopsy (all secondary care).

Top Tips

  • Clarify what patients mean by diarrhoea – they may be referring simply to a minor change in their normal habit or the frequent passage of normal stools.
  • Giardiasis is much more common than previously thought and may be difficult to isolate in stool specimens. Empirical treatment is justified if the clinical picture is suggestive (recent onset after travel of persistent fatty diarrhoea with anorexia, nausea and bloating).
  • IBS rarely causes nocturnal diarrhoea.
  • Patients with gastroenteritis should steadily improve after a few days, but may experience symptoms for up to 10 days – warn them of this.
  • Do not be caught out by overflow diarrhoea in the elderly. The only way to establish this diagnosis is with a PR.
  • Remember to ask about foreign travel and occupation, which have implications for diagnostic possibilities and management.

Red Flags

  • Weight loss in chronic diarrhoea is highly suggestive of significant pathology.
  • In a young and otherwise well person, it is reasonable to make a positive clinical diagnosis of irritable bowel syndrome with minimal investigation – but beware of making this diagnosis for the first time in the middle-aged and elderly. Significant pathology mimicking IBS is likely.
  • Initial telephone consultation is sufficient for most cases of acute diarrhoea, but if in constant (not colicky) abdominal pain, always see and examine to exclude an acute surgical condition.
  • Remember that acute diarrhoea in the elderly can precipitate or aggravate renal failure – especially if they are on ACE inhibitors. Stop these drugs for the duration of the illness and ensure adequate hydration.
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