Excessive Urination

Differential Diagnosis

Common Diagnoses

Occasional Diagnoses

Rare Diagnoses

  • Psychogenic Polydipsia (Compulsive Water Drinking)
  • Supraventricular Tachycardia
  • Didmoad Syndrome (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, Deafness: Autosomal Recessive)
  • Familial Cranial Diabetes Insipidus (Autosomal Dominant Inheritance)
  • Familial Nephrogenic Diabetes Insipidus (Males only: X-Linked Recessive)
  • Fanconi Syndrome

Ready Reckoner

Key distinguishing features of the most common diagnoses

DMDiuretic TherapyCRFAlcoholHigh Ca2+
Marked ThirstYesNoNoNoYes
Other Abnormalities on UrinalysisPossibleNoPossibleNoNo
Abdominal Pain and VomitingPossibleNoNoNoYes
Anorexia/Weight LossYesNoPossibleNoPossible

Possible Investigations

Likely:Urinalysis, fasting glucose or HbA1c.

Possible:FBC, U&E, serum calcium.

Small Print: Blood film, further specialist investigations (see below).

  • Urinalysis: Glucose and possible ketones in diabetes; possible haematuria and proteinuria with renal problems; specific gravity very low in diabetes insipidus and psychogenic polydipsia.
  • Fasting glucose or HbA1c: To confirm diabetes mellitus.
  • FBC: Normochromic anaemia in CKD; film for sickle-cell anaemia.
  • U&E: To detect potassium deficiency and abnormalities suggesting CKD.
  • Serum calcium: Elevated in hypercalcaemia.
  • Further specialist investigations: Many of the aforementioned causes will need further investigation in secondary care to establish underlying aetiology (e.g. ultrasound and renal biopsy in CKD, water deprivation test for diabetes insipidus, CT scan if possible pituitary lesion, and so on).

Top Tips

  • Take time to clarify the symptoms. It is essential to differentiate polyuria from frequency, as the causes are very different.
  • Remember alcohol as a possible cause, especially in young males. Patients can be surprisingly slow to make quite obvious connections.
  • Refer for more detailed investigation if the symptoms are clear-cut and baseline tests draw a blank.

Red Flags

  • Diabetes mellitus is not the only cause of polyuria with thirst. If urinalysis is negative for sugar, consider diabetes insipidus or hypercalcaemia.
  • Weight loss and cough in a smoker with polyuria suggests a possible ACTH-secreting tumour. Arrange an urgent CXR.
  • If urinalysis reveals glucose and ketones in a known or new diabetic, arrange for urgent assessment with a view to admission for stabilisation.
  • Renal disease is likely in patients with polydipsia who have blood and protein on urinalysis.

Published: 2nd August 2022 Updated: 10th April 2024

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