Epidemiology

Hyponatremia is the most common electrolyte disorder encountered in clinical practice.[1][6] It is estimated to occur in 5% to 35% of all hospital inpatients; however, the prevalence varies among studies.[2][3]​​ It should be noted that the serum sodium concentration used to define hyponatremia varies among studies.

In a large, US-based cohort study that assessed over 50,000 hospital admissions, the prevalence of hyponatremia on admission was found to be 37.9%.[7] An additional 38% of patients in this study with a normal initial sodium level developed hyponatremia during admission. Most cases (79%) of hyponatremia in the study were considered to be very mild (i.e., 133-137 mEq/L), 15.2% were mild (128-132 mEq/L), 3.7% moderate (123-127 mEq/L), and 1.7% severe (<122 mEq/L).

In another large, US-based cohort study that assessed over 198,000 hospital admissions, the prevalence of hyponatremia on admission was found to be 5.5%.[8] Other smaller studies have found the prevalence of hyponatremia to range between 7% and 11% in ambulatory outpatients.[9] A retrospective cohort study demonstrated that moderate hyponatremia (125-130 mEq/L) and severe hyponatremia (<125 mEq/L) were present in 2.7% and 1.2% of patients, respectively, on admission to intensive care units.[10] 

Hyponatremia is common in elderly people, especially those who are hospitalized or living in nursing homes.[11]

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