Assessing body water balance in the elderly: Part one
Hyponatraemia is present in approximately one-third of patients presenting to acute hospital care, one-fifth of geriatric nursing home patients and in a reported 7-8% of patients in primary care.
True hypotonic hyponatraemia is due to an excess of body water relative to sodium, caused by water intake that overwhelms renal water excretory capacity.
In the presence of adequate dietary solute intake, the normal kidney can excrete up to 20L of water per day.
Thus, polydipsia is a rare cause of hyponatraemia without coexistent impairment in solute intake.
In most cases of