[Disorders of water balance].

Disorders of water balance are manifested as hyponatremia, polyuria or hypernatremia. While a diagnostic scheme is useful in the exploration of hyponatremia, the urgency of restoration of hyponatremia is essential in the treatment. Regardless of the therapeutic method, strong diuresis is predictive of too rapid restoration of hyponatremia. There are many causes for an increased need to pass urine. Polyuria is in question if the volume of urine collected over a 24-hour period has increased. After excluding diabetes and other common causes of polyuria, the osmolality of the first urine voided in the morning reflects the ability of the kidneys to concentrate urine. A water deprivation test is helpful in the differential diagnosis of the causes of polyuria.