Craving Answers

To the Editor: In their otherwise excellent discussion of a patient with Gitelman’s syndrome, O’Meara et al. (March 3 issue) 1 erroneously stated that an expected urinary sodium level in patients with hyponatremia is less than 40 mmol per liter and that the patient’s urinary sodium level of 136 mmol per liter was inappropriately elevated, given that she had hyponatremia. Hyponatremia is essentially a disorder of water homeostasis rather than a disordered sodium balance. The urinary sodium level is related primarily to volume status and secondarily to daily sodium intake; it does not depend on the serum sodium level. In patients . . .