[Investigations of the urinary sodium excretion in elderly men]

To explore the characteristics of the urinary excretion in the elderly patients and to offer some advice for the prevention and treatment of hyponatremia in the elderly patients.

42 inpatients aged over 80 were divided into tow groups according to their creatinine clearance rate (CCR). Meanwhile, 24 patients aged 45-59 and 31 patients aged 60-79 were chosen as the control groups. All patients were examined 24h urinary electrolytes and CCR.

(1) The CCR in the elderly group was lower than in the middle-aged and old group and the 24 h urinary sodium excretion was accordingly diminished than the two groups. 24 h urinary sodium excretion in CCR abnormal group was also diminished than in CCR normal group. The urinary sodium excretion was not linearly correlate with the CCR in middle-aged group and old group but was linearly correlate in the elderly group. (2) The elderly patients' capability of holding blood sodium and excreting potassium was declined in the CCR normal group. But the urinary excretion of sodium, potassium and phosphonium were all diminished in CCR abnormal group. (3) All patients' sodium intake was higher than the criteria made by China Hypertension Association.

Their urinary sodium excretion is linearly correlate with CCR. Urinary sodium excretion is increased when the elderly patients' renal function is relative normal but when the renal function is severely damaged, urinary sodium excretion is diminished.