Urinary retention: a cause of hyponatremia?

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common cause of hyponatremia in elderly hospitalized patients; however in many patients the etiology remains unclear even after routine investigations.

To report our experience of the association of hyponatremia and urinary retention in elderly hospitalized patients.

Six patients with hyponatremia and urinary retention who were admitted to the geriatric department in our hospital during a four-year period (2001-2004).

The mean age of the patients was 85 years. The mean serum sodium level was 120 mEq/l, average volume of retained urine was 933 ml (range 500-1,500 ml). All patients underwent a comprehensive work-up seeking a possible cause for the hyponatremia. The diagnostic work-up was negative. In 5 of the patients the laboratory findings fulfilled the criteria for SIADH. In all patients hyponatremia resolved following urinary catheterization and fluid restriction. All patients made a complete recovery.

Potentially, urinary retention by itself may cause hyponatremia. The possible mechanism for this is SIADH, triggered by bladder distention or pain due to bladder distention. Urinary catheterization may be the key to treatment in these cases of hyponatremia.