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Impact on Hospitals

The impact of hyponatremia on hospitals:
longer, more costly hospital stays

Hospital-acquired hyponatremia increases length of stay, and the duration of the increase is associated with severity1

In a retrospective analysis of patient cases, hospital-acquired hyponatremia resulted in increases in length of hospital stay that were strongly associated with the severity of hospital-acquired hyponatremia.1

In this retrospective analysis of more than 50,000 hospitalizations (N=29,904) over a 7-year period1:

  • 10,354 cases of hospital-acquired hyponatremia (serum [Na+] <138 mEq/L) developed
  • 16,992 cases of hospitalized patients with normonatremia (serum [Na+] 138-142 mEq/L)
  • Hospital-acquired hyponatremia resulted in a 64% adjusted increase in length of stay (95% CI, 60%-68%)
  • The strength of the association between length of stay and serum sodium increased with decreasing serum sodium (see table below)

Association of hyponatremia severity with hospital length of stay1

Serum [Na+], mEq/L N Odds Ratio 95% CI
138 16,992 1 Reference
<138 10,354 1.64 1.60–1.68
133–137 9,079 1.51 1.48–1.54
128–132 1,187 2.60 2.44–2.76
≤127 88 3.46 3.01–3.98
CI: confidence interval.

Hyponatremia at admission results in longer, more costly stays, with the costliest stays occurring in the more severe cases of hyponatremia2

In this retrospective cohort study of hospitalized patients (aged ≥ 18 years) with hyponatremia (serum [Na+] ≤134 mEq/L) at admission2:

  • 1,500 patients with mild to moderate hyponatremia (serum [Na+] 130-134 mEq/L)
  • 547 patients with moderate to severe hyponatremia (serum [Na+] ≤129 mEq/L)
  • Comparison cohort of 7,573 patients with normonatremia (serum [Na+] 135-145 mEq/L)
  • Patients with mild to moderate and moderate to severe hyponatremia had significantly longer and more costly hospital stays compared to patients with normonatremia (see table below)

Length of Stay and Cost Associated with In-Hospital Hyponatremia2

Hyponatremia LOS and total cost per admission by hyponatremia status adjusted for clinical and demographic variables

Hyponatremia Status N Hospital LOS, Median Days* Total Cost USD*
Moderate to severe (≤129 mEq/L) 547 32 $19,519
Mild to severe (130–134 mEq/L) 1,500 26 $18,054
Normonatremia (135–145 mEq/L) 7,573 22 $17,085

*P<0.001 for Cuzick’s test for trend.
ICU, intensive care unit; LOS, length of stay; USD, US dollars.

The estimated potential burden of hyponatremia for this hospital2:

> 3,400

bed days2

$2.15 Million

in additional hospital costs2

  • Based on an annual admission of approximately 55,000 patients in this study

The estimated potential burden of hyponatremia on the national healthcare system

> 1.4 Million

additional bed days2

$1.1 Billion

in additional costs2

  • Based on the rate of 2.07% for hyponatremia in hospital admissions seen in this study and based on the approximation of an estimated 32 million annual inpatient adult admissions2:
    • Higher cost will be associated with patients requiring ICU care, especially among those with moderate to severe hyponatremia2
    • Hospitals will likely bear the responsibility for these costs. Under most reimbursement methodologies, hospitals are unable to bill patients or payers for these extended hospital stays2

Both hyponatremia at admission and hospital-acquired hyponatremia result in increases in ICU admissions and hospital readmissions, as well as a greater utilization of healthcare resources3

A retrospective observational study of 36,048 patients that had been discharged from 445 hospitals3:

  • 18,024 patients with a primary diagnosis of hyponatremia were matched with 18,024 patients without a primary or secondary diagnosis of hyponatremia
  • Patients with hyponatremia had a 7.6% increase in length of stay (95% CL: 6.2%, 9.1%; P<0.001)
  • Hyponatremia resulted in a mean increase in hospital costs of 8.9% (95% CL: 7.5%, 10.4%; P<0.001)
  • Primary diagnosis of hyponatremia was associated with an increased risk of ICU admission (OR, 1.89; 95% CL: 1.72, 2.07; P<0.001)
  • Primary diagnosis of hyponatremia was associated with an increased risk of hospital readmission within 30 days for hyponatremia (OR, 4.76; 95% CL: 4.31, 5.26; P<0.001)

CL: confidence limit; OR: odds ratio.

The 3 Types of Hypotonic Hyponatremia

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