Polyuria is an increase in total daily output of urine. Urine output more than 2000 ml/m2/ 24 hrs is defined as polyuria.
It needs to be distinguished from increased frequency of micturition, nocturia and enuresis. These conditions might not be always associated with increase in total daily urine output.
Daily urine productions depends upon amount of solute and water ingested or produced from metabolism in excess of body requirement and renal concentrating capacity, which is regulated by antidiuretic hormone (ADH) and renal medullary interstitium.
Polyuria may be due to solute diuresis (urine osmolality >250 mOsm/Kg) or water diuresis (urine osmolality <250 mOsm/Kg)
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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