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Impact of Hyponatremia Correction on the Risk for 30-Day Readmission and Death in Patients with Congestive Heart Failure


The study objective was to compare the 30-day readmission rate and mortality between patients with heart failure who have persistent hyponatremia during hospitalization and patients who have their admission hyponatremia corrected before discharge.


This large retrospective cohort study included all adult patients admitted with a diagnosis of congestive heart failure to a tertiary-care hospital between July 2003 and October 2009. We compared the readmission rate and mortality 30 days after discharge between patients with persistent hyponatremia (ie, low sodium level at both admission and discharge) and patients with hyponatremia correction during hospitalization.


Among the 4295 eligible patients with hyponatremia at admission, 1799 (41.9%) did not have their sodium level corrected at discharge. Overall, 1269 patients (29.5%) had a 30-day unplanned readmission or died. In a multivariable logistic regression analysis, the absence of hyponatremia correction was associated with a 45% increase in the odds of having a 30-day unplanned readmission or death (odds ratio, 1.45; 95% confidence interval, 1.27-1.67). Among patients with persistent hyponatremia, those with more severe hyponatremia at discharge (<130 mm/L) had a higher odds (odds ratio, 1.68; 95% confidence interval, 1.32-2.14) of having a 30-day readmission or death than those with less severe hyponatremia at discharge (130-134 mm/L).


The absence of correction of hyponatremia over the course of hospitalization was frequent and independently associated with an increase of approximately 50% in the odds of having a 30-day unplanned readmission or death. This association appeared to be independent of heart failure severity.

Hyponatremia is present at admission in approximately 20% to 30% of the patients hospitalized for heart failure and is associated with an increased risk for readmission and death in patients with congestive heart failure compared with patients with congestive heart failure without hyponatremia at admission. However, the prognostic impact of persistent hyponatremia throughout the hospitalization has not been explored to the same extent.

One study found that the change in sodium level after hospital discharge was a strong predictor of long-term survival in patients with heart failure; however, little is known in terms of the impact of sodium changes during the hospitalization. Two small post hoc analyses of randomized control trials found conflicting results in terms of mortality risk and may not truly represent the general heart failure population.

Our hypothesis was that patients with heart failure with persistent hyponatremia would be at higher risk for worse postdischarge outcomes than those with corrected sodium levels. Therefore, we compared the 30-day readmission rate and mortality after discharge between patients with persistent hyponatremia and patients with hyponatremia correction during hospitalization.

Materials and Methods

Design and Setting

The study was designed as a retrospective cohort study and conducted at Brigham and Women’s Hospital, Boston, Massachusetts, which is a large tertiary referral center and teaching hospital with approximately 750 beds. The study was approved by the institutional review board, and patient consent was waived. Our study followed Strengthening of Reporting Observational Studies in Epidemiology guidelines.16


All adult (aged ≥18 years) inpatients with congestive heart failure, admitted after June 30, 2003, and discharged before November 1, 2009, were identified. Diagnosis of congestive heart failure was identified by International Classification of Diseases, Ninth Revision (ICD-9), World Health Organization, Geneva, Switzerland: 402.01, 402.11, 402.91, 404.01, 404.03, 404.11, 404.13, 404.91, 404.93, 428.0-428.9. All types of heart failure were included, without differentiating between heart failure with preserved and reduced ejection fraction. Only patients with a hyponatremia at admission were included, defined as a sodium level of less than 135 mmol/L at admission. Patients were excluded if they stayed ≤24 hours at the hospital, died during the hospitalization, were transferred to another hospital or care center, or left the hospital against medical advice.


The primary outcome was any nonelective hospital readmission or all-cause death within 30 days after hospital discharge. Readmissions to the same hospital network were captured using the electronic health record. We used the Social Security Death Index to identify the patients who died within 30 days after the discharge date. Secondary outcomes included each single component of the primary outcome separately and any 30-day unplanned readmission due to congestive heart failure.


The exposure of interest was the correction of hyponatremia during the hospital course and was grouped into 2 categories: (1) hyponatremia was persistent over the hospital stay, defined as a sodium level <135 mmol/L at both admission and discharge; and (2) the hyponatremia was corrected during the hospitalization, defined as a sodium level <135 mmol/L at admission, but ≥135 mmol/L at discharge.

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-Jacques D. Donzé, MD, MS, Patrick E. Beeler, MD∗, David W. Bates, MD, MSc

This article originally appeared in the August 2016 issue of The American Journal of Medicine.

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