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Mortality Risks

Hyponatremia mortality risks

Hyponatremia significantly increases mortality risk in hospitalized patients.1 In a meta-analysis of 81 studies (N=850,222) comparing mortality in patients with hyponatremia (n=147,948) and without hyponatremia1:

  • Hyponatremia is significantly associated with an increased overall mortality risk
    • Relative risk 2.60 [2.31-2.93], P<0.0001

Hospital-acquired hyponatremia is associated with a greater incidence of in-hospital mortality2

In a retrospective analysis of 53,236 hospitalizations from 7 years of patient discharge records2:

  • Out of 27,897 hospitalizations with normonatremia (serum [Na+]: 138-142 mEq/L) on admission, and a hospital length of stay longer than 1 day, hospital-acquired hyponatremia developed in 10,662 hospitalizations
  • Hospital-acquired hyponatremia was associated with twice the incidence of in-hospital mortality:
    • Hyponatremia: 2.9%
    • Normonatremia: 1.4%
  • Hospital-acquired hyponatremia was associated with a 66% increase in adjusted odds of in-hospital mortality (OR, 1.66; 95% CI, 1.39-1.98), and this association increased with decreasing serum sodium concentrations

Impact of Hospital-Acquired Hyponatremia* on Mortality

Risk of mortality continues after hospitalization3

In a 3-year, prospective cohort analysis that assessed the risk of postdischarge mortality in in-hospital hyponatremia at 2 academic teaching hospitals in Boston, Massachusetts3:

  • Hyponatremia (serum [Na+]<135 mEq/L) was observed among 14.5% of the 98,411 patients studied
  • Patients with hyponatremia had higher 1- and 5-year mortality rates compared to patients without hyponatremia
    • Multivariable-adjusted mortality risk at 1 year increased by 38%
    • Multivariable-adjusted mortality risk at 5 years increased by 25%
  • Even mild in-hospital hyponatremia (serum [Na+] =130-134 mEq/L) carried an increased risk of mortality after discharge
    • Multivariable-adjusted mortality risk at 5 years postdischarge increased by 24% (P<0.001)
  • Mortality risk was much lower in patients who had their hyponatremia resolved during hospitalization
    • Multivariable-adjusted 1-year postdischarge mortality risk: 19% for resolved hyponatremia versus 55% for persistent hyponatremia
    • Multivariable-adjusted 5-year postdischarge mortality risk: 18% for resolved hyponatremia versus 32% for persistent hyponatremia

Patients with hyponatremia had higher in-hospital and postdischarge mortality rates than patients with normal serum sodium concentrations3

Serum sodium 135-144 mEq/L <135 mEq/L
Mean age (years) 63.1 67.0
Crude in-hospital mortality (%) 2.4 5.4
Crude 1-year mortality (%) 11.7 21.4
Crude 5-year mortality (%) 42.3 54.8
Adapted from Waikar SS, et al. Am J Med. 2009;122(9):857-865.

Hyponatremia on admission increases mortality risk of hospitalized patients with heart failure4

In a retrospective analysis of 115,969 patients hospitalized for acute decompensated heart failure4:

  • Hyponatremia (serum [Na+] =131-135 mEq/L) was present in 15.9% (n=18,445) of patients at admission
  • Severe hyponatremia (serum [Na+] ≤130 mEq/L) was present in 5.3% (n=6,117) of patients at admission
  • Hospital mortality rate was significantly higher in patients with severe hyponatremia and hyponatremia compared to patients with normonatremia
    • Normonatremia: 2.9%
    • Hyponatremia: 4.9%, P<0.0001*
    • Severe hyponatremia: 7.6%, P<0.0001*
  • Multiple regression analysis of mortality found that serum sodium abnormalities were independently associated with increased mortality risk compared to normonatremia
    • Hyponatremia: OR, 1.29; 95% CI, 1.19-1.40
    • Severe hyponatremia: OR, 1.78; 95% CI, 1.59-1.99

*Compared to normonatremia.
CI: confidence interval; OR: odds ratio.

In an analysis of the relationship between serum sodium and clinical outcomes in patients participating in the Organized Program to Initiate Lifesaving Treatment in Hospitalized Patients with Heart Failure (OPTIMIZE-HF) registry5:

  • 19.7% (n=9,368) of the 47,647 heart failure patients had hyponatremia (serum [Na+] <135 mEq/L) at the time of admission
  • Overall in-hospital mortality rate for patients with hyponatremia was significantly (P<0.0001) greater than those with normonatremia
    • Normonatremia: 3.2%
    • Hyponatremia: 6%
  • The risk for in-hospital mortality began to rise with an admission serum sodium concentration below 138 mEq/L and was more than double in the 132-135 mEq/L range

Relationship between admission serum sodium levels and in-hospital mortality
in patients with heart failure5

The 3 Types of Hypotonic Hyponatremia

Watch videos discussing the definitions, etiologies, and pathogenesis of hypovolemic, euvolemic, and hypervolemic hyponatremia.