• Mark A Callahan, Huong T Do, David W Caplan, and Kahyun Yoon-Flannery.
• Weill Cornell Medical College, Division of Outcomes and Effectiveness Research, Department of Public Health, New York, NY, USA. mcallahan@fojp.com
• Postgrad Med. 2009 Mar 1; 121 (2): 186-91.

BackgroundHyponatremia is the most common electrolyte abnormality seen in general hospital patients, with an incidence of 1% to 6% in the United States.ObjectiveWe aimed to evaluate the impact of varying levels of hyponatremia at admission on length of stay (LOS) and cost of care in adult hospitalized patients.MethodsA retrospective cohort study was conducted using an existing clinical database from a large academic-setting hospital. All adult admissions from January 2004 through May 2005 with serum sodium level at admission of < or = 134 mEq/L were separated into 2 cohorts: patients with moderate-to-severe hyponatremia (serum sodium level at admission of < or = 129 mEq/L, n = 547) and patients with mild-to-moderate hyponatremia (serum sodium level of 130-134 mEq/L, n = 1500). ICD-9 diagnosis codes for these 2047 admissions with hyponatremia were used to identify a cohort of 7573 admissions with the same principal admitting diagnoses and a serum sodium level of 135 to 145 mEq/L. Differences in hospital LOS, intensive care unit (ICU) admission rate, and median total costs per admission between cohorts were examined using multiple linear regression, logistic, and quantile regression models.ResultsAdmissions with hyponatremia had significantly longer hospital LOS than those admitted without hyponatremia (median LOS: moderate-to-severe hyponatremia, 8 days; mild-to-moderate hyponatremia, 8 days; normal, 6 days; P < 0.001). Patients with more severe hyponatremia were also more likely to be admitted to the ICU during the hospital stay (moderate-to-severe hyponatremia, 32%; mild-to-moderate hyponatremia, 26%; normal, 22%; P < 0.001). These trends were also reflected in the total costs per admission, with median costs of $16,606 for moderate-to-severe hyponatremia cases, $14,266 for mild-to-moderate hyponatremia cases, and $13,066 for normal admissions (P < 0.001).ConclusionsHyponatremia at admission was associated with increased LOS and cost of care for hospitalized patients. Interventions or pharmacotherapies for the prompt treatment of hyponatremia could potentially reduce morbidity and LOS, thereby reducing the utilization of health care resources.

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