Paediatrics: Polyuria and frequency

Polyuria and frequency

This is often subjective and difficult to assess, particularly in small children. Frequency can be considered to be the inappropriate and frequent pas-sage of small amounts of urine. Polyuria can be quantitatively defined as the passage of greater than 2000mL/1.73m² per 24hr period.

Assessment of polyuria and frequency requires a detailed history of uri-nary frequency habit.

Causes of polyuria

•   Renal disorders:

o chronic kidney disease;

o post-obstructive uropathy;

o nephrogenic diabetes insipidus;

o Fanconi syndrome.

•   Metabolic/endocrine disorders:

o diabetes mellitus;

o cranial diabetes inspidus;

o hypoadrenalism.

·  Excess and inappropriate water intake: psychogenic polydipsia.

Causes of urinary frequency

•   Urinary tract infection.

•   Bladder irritability and instability.

•   All causes of polyuria.

•   Small bladder capacity.

Investigations

Baseline screening investigations should include the following.

Urine

•   Urinalysis by urine dipstick testing.

•   Urine culture.

•   Urine osmolality.

Blood

•   Urea and electrolytes.

•   Plasma osmolality.

•   Blood glucose (random or fasting).