Association of hyponatremia with in-hospital mortality in cardiac ward patients: a retrospective analysis

Aim. To identify risk factors of in-hospital mortality in patients with hyponatremia in a cardiology hospital setting.
Material and methods. This single-center retrospective study included 119 patients (mean age 71.2±12.7 years) admitted to a cardiology center from June 2024 to March 2025, who had at least one recorded instance of hypotonic hyponatremia (sodium level <135 mmol/L). Patients with acute coronary syndrome and myocardial infarction were excluded. Statistical analysis was performed using logistic regression and ROC analysis.
Results. The prevalence of hyponatremia was 4.1%. In-hospital mortality reached 16.0% (19 deaths). Hypervolemic hyponatremia, typical for patients with chronic heart failure, was the most common type (48.7%). According to multivariable regression analysis, factors associated with in-hospital mortality were minimum sodium level (OR 0.843; 95% СI 0.749-0.950; p=0.005), glomerular filtration rate (OR 0.957; 95% СI 0.921-0.991; p=0.021), and left ventricular ejection fraction (OR 0.949; 95% СI 0.907-0.994; p=0.027). The constructed predictive model demonstrated good discriminative ability: AUC=0.851 with sensitivity of 78.6%, specificity of 76.7%, and overall accuracy of 77.0%.
Conclusion. Minimum serum sodium level is a risk factor of in-hospital death, particularly in patients with reduced glomerular filtration rate and left ventricular ejection fraction. 

1. Spasovski G, Vanholder R, Allolio B, et al.; Hyponatraemia Guideline Development Group. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014;170(3):G1-47. DOI:10.1530/EJE-13-1020. Erratum in: Eur J Endocrinol. 2014;171(1):X1.

2. Ternero-Vega JE, Jiménez-de-Juan C, Castilla-Yelamo J, et al. Impact of hyponatremia in patients hospitalized in Internal Medicine units: Hyponatremia in Internal Medicine units. Medicine (Baltimore). 2024;103(21):e38312. DOI:10.1097/MD.0000000000038312.

3. Shchekochikhin DY, Kozlovskaya NL, Kopylov FY, et al. Hyponatremia: A clinical approach. Terapevticheskii arkhiv. 2017;89(8):134-40. (In Russ.)

4. Ayus JC, Achinger SG, Arieff A. Brain cell volume regulation in hyponatremia: role of sex, age, vasopressin, and hypoxia. Am J Physiol Renal Physiol. 2008;295(3):F619-24. DOI:10.1152/ajprenal.00502.2007.

5. Ayus JC, Moritz ML. Hyponatremia Treatment Guidelines — Have They Gone Too Far? NEJM Evid. 2023;2(4):EVIDe2300014. DOI:10.1056/EVIDe2300014.

6. Achinger SG, Ayus JC, Kumar A, Tsalatsanis A. Thiazide-Associated Hyponatremia and Mortality Risk: A Cohort Study. Kidney Med. 2024;7(2):100941. DOI:10.1016/j.xkme.2024.100941.

7. Sumi H, Tominaga N, Fujita Y, Verbalis JG; and the Electrolyte Winter Seminar, Collaborative Group. Pathophysiology, symptoms, outcomes, and evaluation of hyponatremia: comprehension and best clinical practice. Clin Exp Nephrol. 2025;29(2):134-48. DOI:10.1007/S10157-025-02624-9.

8. Otterness K, Singer AJ, Thode HC Jr, Peacock WF. Hyponatremia and hypernatremia in the emergency department: severity and outcomes. Clin Exp Emerg Med. 2023;10(2):172-80. DOI:10.15441/ceem.22.380.

9. Shekar RG, Rodha MS, Sharma A, et al. Short-Term Outcomes of Patients With Hyponatremia Presenting to the Emergency Department: An Observational Study. Cureus. 2024;16(7):e63679. DOI:10.7759/cureus.63679.

10. Singh B, Mod U, Shah M, et al. Outcome of hyponatremia in critically ill patients. Indian J Appl Basic Med Sci. 2020;12(1):11-7. DOI:10.48165/ijabms.2020.22103

11. Isaak J, Boesing M, Potasso L, et al. Diagnostic workup and outcome in patients with profound hyponatremia. J Clin Med. 2023;12(10):3567. DOI:10.3390/jcm12103567.

12. Garrahy A, Cuesta M, Murphy B, et al. Active management of severe hyponatraemia is associated with improved mortality. Eur J Endocrinol. 2021;184(1):9-17. DOI:10.1530/EJE-20-0909.

13. Courtney A, Joyce Tan LY, Elsheikh A, et al. Characteristics, management and outcomes of patients with hyponatraemia presenting to an Irish tertiary hospital. Endocr Connect. 2025;14(4):e240666. DOI:10.1530/EC-24-0666.