Severity Increases Hospital Mortality in Hyponatraemia

TOPLINE:

Patients with hyponatraemia exhibited higher 30-day mortality rates than those with normal sodium concentrations, and over time, the risk for mortality declined among patients with mild hyponatraemia; however, this trend was less pronounced in those with moderate hyponatraemia and absent in those with severe hyponatraemia.

METHODOLOGY:

• Researchersanalysed the risk for mortality related to sodium concentrations in 79,407 individuals from the Stockholm Sodium Cohort who were admitted to medical wards (internal medicine, cardiology, or geriatric facilities) and had serum sodium concentrations ≤ 145 mmol/L after admittance.
• Patients were categorised on the basis of their sodium concentrations as those with mild (130-134 mmol/L), moderate (125-129 mmol/L), profound (120-124 mmol/L), and very profound (< 120 mmol/L) hyponatraemia.
• After propensity score matching, mortality rates were compared between patients (n = 66,941; 52.7% women) with varying levels of hyponatraemia and those with normal sodium concentrations (135-145 mmol/L).
• Primary causes of death after baseline were identified in the Swedish Cause of Death Register and coded according to the International Statistical Classification of Diseases and Related Health Problems, Version 10 diagnosis of hyponatraemia.

TAKEAWAY:

• Patients with hyponatraemia had increased 30-day mortality rates, which increased with the severity of hyponatraemia (hazard ratio [HR], 1.35; 95% CI, 1.28-1.42 in mild hyponatraemia; HR, 3.38; 95% CI, 2.16-5.28 in very profound hyponatraemia).
• Mortality rates at 1 year showed minimal elevation in mild hyponatraemia (HR, 1.04; 95% CI, 1.01-1.07) but increased with the severity of the condition (HR, 1.18-1.37).
• Cancer and circulatory diseases were the leading causes of death within 30 days of hospitalisation, whereas conditions related to hyponatraemia, such as osmotic demyelination syndrome, falls, and fractures, had minimal impact on the overall mortality; for mild to profound hyponatraemia, excess mortality was primarily attributed to neoplasms and gastrointestinal disorders, particularly liver diseases, along with circulatory disorders.

IN PRACTICE:

“Short-term mortality is higher in patients with hyponatraemia than in matched counterparts with normal sodium concentrations, whereas long-term mortality patterns vary by degree of hyponatraemia,” the authors wrote.

SOURCE:

This study was led by Buster Mannheimer and Jonatan D. Lindh, Karolinska Institutet, Stockholm, Sweden. It was published online on April 15, 2025, in the European Journal of Internal Medicine.

LIMITATIONS:

Differences in mortality between sodium strata may be affected by residual confounding due to varying comorbid burdens. The study focused solely on sodium concentrations at admission, without tracking changes over time. Primary causes of death did not fully capture all factors contributing to mortality.

DISCLOSURES:

One author reported receiving support from the Värmland’s County Research Council and the Swedish Society of Medicine. The authors reported having no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.