Approach a child with polyuria

Previous Post: What is Polyuria

While evaluating a child with suspected polyuria, first step is to confirm polyuria by measuring the 24 hour urine output. 

Once confirmed detailed history should be obtained about-

  • 24 hour fluid intake,
  • Type of fluids ingested,
  • Eating habits,
  • Drinking through day or night,
  • Weight gain/loss,
  • Episodes of dehydration,
  • Constipation etc. 

In Examination look for –

  • Signs of failure to thrive,
  • Dehydration,
  • Rickets

Next step is to do some basic investigations:

Blood tests for

  • Serum Osmolality,
  • Serum sodium, potassium,
  • Blood glucose,
  • Calcium,
  • Urea,
  • Creatinine.

Urinalysis (first morning urine) for

  • Osmolality,
  • Specific gravity
  • Glucose


  • Serum osmolality                                              285 to 295 mOsm/kg
  • Random urine osmolality                                300-900m mOsm/kg
  • Urine, after 12-14 hrs water deprivation > 850   mOsm/kg

Next Post : How to differentiate a true polydipsia or polyuria from psychogenic polydipsia

Post Pic credits Dr Sue Jones, Consultant Physician & Honorary Senior Clinical Lecturer, RCP, London

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.