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

NORMAL OSMOLALITY RANGES

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

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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