Sodium levels on admission are associated with mortality risk in hospitalized patients

Abnormal sodium values are common among hospitalized patients. We aimed to investigate the association of admission sodium values and mortality.

Historical prospectively data of adult patients hospitalized to medical wards between January 2011 and December 2013. Admission sodium values were classified to five categories: severe hyponatremia (<125mEq/L), mild hyponatremia (125-135mEq/L), normal sodium values (135-145mEq/L), mild hypernatremia (145-150mEq/L) and severe hypernatremia (>150mEq/L). Main outcomes were length of hospitalization, in-hospital mortality and mortality at the end-of-follow-up.

The cohort included 27,889 patients (mean age 67±18years, 52% males). The total follow-up was 1065days. Most patients had normal sodium values (76%), 22% had hyponatremia, 3% had hypernatremia. Mean age increased with increase in severity of hyponatremia or hypernatremia. Median length of hospitalization was longer with mild and severe hypernatremia (7 and 5days, respectively) or with mild and severe hyponatremia (4 and 4days, respectively), compared to normal sodium levels (3days). Compared to in-hospital mortality with normal sodium levels (5%), mortality was higher with mild and severe hyponatremia (9% and 14%, respectively) and was highest with mild (28%), and severe hypernatremia (52%). Mortality rate at the end of follow-up was 28% with normal sodium levels, 44% and 48% with mild and severe hyponatremia, 66% and 90% with mild and severe hypernatremia, respectively.

Abnormal sodium values on admission were associated with longer hospitalization and increased short- and long-term mortality. Mortality risk was higher with hypernatremia, compared to hyponatremia.