Diarrhoea in Children

Differential Diagnosis

Common Diagnoses

  • Gastroenteritis
  • Other Systemic Infection (e.g. UTI, Otitis Media, Pneumonia)
  • Toddler’s Diarrhoea
  • Medication Side Effects (Usually Antibiotics)
  • Cow’s Milk Protein Allergy (CMPA)

Occasional Diagnoses

  • Lactose Intolerance (Typically Following a Bout of Gastroenteritis in Babies)
  • Faecal Impaction (Causing Overflow Diarrhoea)
  • Irritable Bowel Syndrome
  • Coeliac Disease
  • Other Gastrointestinal Infections, e.g. Giardia

Rare Diagnoses

  • Inflammatory Bowel Disease (IBD)
  • Appendicitis (Relatively Common but Rarely Presents with Diarrhoea)
  • Intussusception
  • Cystic Fibrosis

Ready Reckoner

Key distinguishing features of the most common diagnoses

GastroenteritisOther Systemic InfectionToddler’s DiarrhoeaMedication Side EffectsCMPA
Blood in DiarrhoeaPossibleNoNoNoPossible
Recent or Current AntibioticsNoPossibleNoYesNo
Lasts More than 2 WeeksPossibleNoYesPossibleYes
Other Localising Symptoms (e.g. Respiratory, Urinary or Ear)NoYesNoPossibleNo

Possible Investigations


Possible:Stool culture, urinalysis, MSU, FBC, CRP, ESR, anti-endomysial and anti-gliadin antibodies, faecal calprotectin.

Small Print:Hospital-based tests (e.g. for cystic fibrosis, IBD and to confirm coeliac disease).

  • Stool culture: For microbiological examination if the diarrhoea persists more than a week, is bloody or there is relevant recent foreign travel; send three specimens for ova, cysts and parasites if giardia suspected.
  • Urinalysis: May help if a UTI is suspected as the underlying cause.
  • MSU: For confirmation of a suspected UTI.
  • FBC, ESR, CRP: Hb may be reduced, and CRP/ESR raised in IBD.
  • Anti-endomysial and anti-gliadin antibodies: If coeliac is a possibility.
  • Faecal calprotectin: To help rule out IBD if diarrhoea is prolonged.
  • Hospital-based tests: These might include endoscopy and biopsy in suspected IBD or coeliac disease, and tests for possible cystic fibrosis.

Top Tips

  • It is not unusual for the diarrhoea in gastroenteritis to take a couple of weeks to settle; consider a stool specimen if it is not starting to improve after a week.
  • Don’t overlook faecal impaction as a cause of overflow diarrhoea in children, the clues being soiling and a preceding history of constipation.
  • Lactose intolerance tends to be over-diagnosed and often confused with CMPA. The former is less common, typically follows gastroenteritis and is usually short lived.
  • Undigested food (‘peas and carrots syndrome’) in the persistent loose stool of an otherwise well and thriving child is virtually pathognomic of the harmless toddler’s diarrhoea.

Red Flags

  • In the acute case – particularly in younger children with severe diarrhoea and associated vomiting – assess for dehydration as a priority. If the child is significantly dehydrated, then admission will be needed regardless of cause.
  • Bloody diarrhoea raises the stakes somewhat. In the acute situation, this could be one of the more severe forms of gastroenteritis or, especially in those under 1 year of age, intussusception. In more prolonged cases, it might indicate CMPA or IBD.
  • Very minor, transient weight loss is common during a bout of gastroenteritis. More prolonged weight loss with persistent diarrhoea should, on the other hand, prompt urgent referral.
  • Remember that appendicitis can cause diarrhoea. In such cases, the abdominal pain is usually more marked and constant than in a typical gastroenteritis, where it is typically mild (and therefore not the presenting complaint) and intermittent.
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