Prognostic implications of hyponatremia in elderly hospitalized patients.

Hyponatremia is the most common electrolyte imbalance in elderly in-patients. We hypothesized that hyponatremia was independently associated with increased length of stay and loss of independence or death as measured by failure to return to previous residence. This cohort study measured the prognostic impact of hyponatremia in all patients admitted to two acute geriatric wards. Basic demographic data and serum sodium results were included in multiple linear and logistic regression models for the end-points length of stay and return to previous residence respectively. There were 103 cases (mean age 82, 59% female), of whom 19 (18%) were hyponatremic on admission, but another 24 (23%) became hyponatremic whilst in hospital. Median length of stay was 13 days. Sixty-six (65%) cases returned to the previous residence on discharge, 8 (8%) patients died. Factors independently associated with longer length of stay were increasing age (p=0.016), lower admission serum sodium (p=0.012) and larger drop in serum sodium during the admission (p<0.001). Only a larger drop in serum sodium was significantly associated with failure to return to previous residence (p<0.001). We conclude that hyponatremia in elderly in-patients is common. Drop in serum sodium during admission was strongly associated with increased length of stay and loss of independence.