Differential Diagnosis

Common Diagnoses

Occasional Diagnoses

Rare Diagnoses

  • Gastroduodenal Disease (e.g. Pyloric Stricture or Stenosis, Du, Carcinoma)
  • Meningitis
  • Cerebral Haemorrhage
  • Bulimia Nervosa
  • Severe Constipation
  • Raised Intracranial Pressure (e.g. Tumour)
  • Renal Failure
  • Acute Glaucoma

Ready Reckoner

Key distinguishing features of the most common diagnoses

GastroenteritisVestibular NeuronitisURTI (Child)PregnancyAcute Abdomen
Mainly Mornings No No NoYes No
With DiarrhoeaYes NoPossible NoPossible
Nystagmus NoYes No No No
Bowel Sounds Increased?Yes No No NoPossible
Tender Abdomen?Possible NoPossible NoYes

Possible Investigations


Possible:Urinalysis, MSU, pregnancy test, blood glucose, FBC, U&E.

Small Print:Lumbar puncture, abdominal X-rays, renal imaging, OGD, CT scan.

  • Urinalysis: High specific gravity suggests dehydration; glucose and ketones indicate hyperglycaemia; blood, pus cells and nitrites suggest UTI (confirm with MSU); blood alone might indicate a renal stone.
  • Pregnancy test: To confirm or reveal pregnancy.
  • Blood glucose: Will confirm hypo- or hyperglycaemia.
  • U&E: May be deranged by vomiting; may also reveal underlying renal failure.
  • FBC: Raised WCC suggests underlying infection or inflammation. Haemoglobin (Hb) may be reduced in malignancy. Raised platelets associated with oesophageal or stomach cancer.
  • Lumbar puncture, renal imaging, abdominal X-rays, OGD and CT scans: Required in a few cases depending on the clinical picture and invariably arranged by the relevant specialist.

Top Tips

  • Vomiting in children tends to be presented early, when it may be difficult to give a definite diagnosis. Be honest about this and make sure that parents know to call you again if the symptom doesn’t settle or other ‘alarm’ symptoms develop – or arrange a definite time for follow-up.
  • Remember to look for both the cause (i.e. the aetiology) and the effect (i.e. possible dehydration) – especially in the very young and the very old, when the history may be difficult to obtain and the effects of fluid loss more marked.
  • Check to see if the patient is on any medication. This may be causing the vomiting, or it may have serious implications for management (e.g. steroids).
  • Don’t forget pregnancy as a cause – the patient may be ‘ignoring’ the possibility.

Red Flags

  • Unless the diagnosis is obviously migraine, beware the patient with vomiting and a headache – think of meningitis, subarachnoid haemorrhage or raised intracranial pressure.
  • Do not treat empirically with anti-emetics – these may mask the true diagnosis or cause diagnostic confusion via side effects.
  • Have a low threshold for admitting diabetics. Whatever the cause of the vomiting, their diabetes is liable to become uncontrolled.
  • Look for acid dental erosion as a clue to bulimia in recurrent vomiting.
  • Gastroenteritis should cause increased bowel sounds. In the patient with abdominal pain and vomiting, if bowel sounds are absent or scanty, the diagnosis is likely to be an acute abdomen.

Published: 1st August 2022 Updated: 10th April 2024

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