Hyponatremia, defined as a serum sodium concentration of less than 135 mEq/L, is the most common electrolyte disorder encountered in clinical practice and affects patients across a wide spectrum of medical and surgical conditions [1,2]. It is particularly prevalent among hospitalized and elderly patients, with reported incidence ranging from 15% to 30% depending on the study population [3,4]. Hyponatremia results from an imbalance in water homeostasis rather than sodium deficiency alone and may arise from various conditions such as syndrome of inappropriate antidiuretic hormone secretion (SIADH), heart failure, liver cirrhosis, chronic kidney disease, endocrine disorders, gastrointestinal losses, and the use of medications including diuretics [5]. The clinical manifestations vary from mild nonspecific symptoms such as fatigue, nausea, and headache to severe neurological complications including seizures, coma, and death, depending on the severity and rapidity of onset [6].

The underlying etiology of hyponatremia is often multifactorial, making accurate diagnosis and appropriate management challenging [7]. A systematic clinical assessment combined with laboratory evaluation, including serum and urine osmolality, urine sodium concentration, and assessment of volume status, is essential to identify the underlying cause and guide treatment [8]. Early recognition is particularly important because inappropriate correction or delayed treatment may lead to serious complications such as osmotic demyelination syndrome or persistent neurological dysfunction [9]. Therefore, determining the etiology of hyponatremia is a critical step in improving patient outcomes.

Several studies have demonstrated that hyponatremia is independently associated with increased morbidity, prolonged hospital stay, greater need for intensive care, higher healthcare costs, and increased mortality [10]. Severe hyponatremia has been linked to adverse outcomes including respiratory failure, cognitive impairment, falls, fractures, and poor prognosis in patients with cardiovascular, renal, hepatic, and neurological diseases [11,12]. However, the spectrum of etiological factors and their relationship with clinical outcomes varies across different populations due to differences in demographics, comorbidities, prescribing practices, and healthcare settings [12]. Consequently, institution-specific data are valuable for understanding local disease patterns and optimizing management strategies.

The present study aimed to evaluate the etiological profile of hyponatremia in adult patients and to assess the clinical outcomes associated with different causes and severities of hyponatremia in a tertiary care hospital.

MATERIALS AND METHODS

This prospective observational study was conducted in the Department of General Medicine of a tertiary care teaching hospital over a period of one year, from May 2024 to May 2025. A total of 120 consecutive adult patients (≥18 years) diagnosed with hyponatremia (serum sodium <135 mEq/L) at admission or during hospitalization were enrolled after obtaining approval from the Institutional Ethics Committee. Written informed consent was obtained from all participants or their legally authorized representatives prior to inclusion in the study.

Adult patients with documented hyponatremia who consented to participate were included in the study. Patients with pseudohyponatremia due to severe hyperlipidemia or paraproteinemia, those with hypertonic hyponatremia secondary to marked hyperglycemia or osmotic agents, patients with incomplete clinical or laboratory records, and those unwilling to participate were excluded. Demographic details, presenting complaints, medical history, drug history (particularly diuretic use), comorbid illnesses, physical examination findings, and volume status assessment were recorded using a predesigned case record form.

All patients underwent detailed laboratory evaluation including serum sodium, potassium, chloride, blood urea, serum creatinine, blood glucose, serum osmolality, urine sodium, and urine osmolality whenever clinically indicated. Additional investigations such as thyroid function tests, serum cortisol, liver function tests, chest radiography, electrocardiography, ultrasonography, echocardiography, and computed tomography or magnetic resonance imaging were performed when required to identify the underlying etiology. Hyponatremia was classified as mild (130–134 mEq/L), moderate (125–129 mEq/L), or severe (<125 mEq/L). The etiology was established based on clinical findings, laboratory investigations, and standard diagnostic criteria, including syndrome of inappropriate antidiuretic hormone secretion (SIADH), diuretic-induced hyponatremia, congestive heart failure, chronic kidney disease, chronic liver disease, gastrointestinal losses, endocrine disorders, and other identifiable causes.

Patients received treatment according to the underlying cause and severity of hyponatremia, including fluid restriction, isotonic saline, hypertonic saline, oral salt supplementation, vasopressin receptor antagonists, and correction of the precipitating condition. Clinical outcomes including requirement for intensive care unit admission, mechanical ventilation, duration of hospital stay, correction of serum sodium, and in-hospital mortality were recorded. Data were entered into Microsoft Excel and analyzed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA). Continuous variables were expressed as mean ± standard deviation, while categorical variables were presented as frequencies and percentages. Comparisons between groups were performed using the independent Student's t-test or one-way ANOVA for continuous variables and the Chi-square test or Fisher's exact test for categorical variables, as appropriate. A p value of <0.05 was considered statistically significant.

RESULTS

A total of 120 adult patients with hyponatremia were included in the study. The mean age of the participants was 59.8 ± 16.2 years, with nearly half (47.5%) aged above 60 years. Males constituted 56.7% of the study population. Generalized weakness was the most common presenting symptom (74.2%), followed by nausea/vomiting (43.3%), altered sensorium (34.2%), confusion (30.8%), and dizziness (27.5%). Seizures were observed in 15.0% of patients. (Table 1).

Table 1. Baseline Characteristics and Clinical Presentation of Patients with Hyponatremia (N=120)

Moderate hyponatremia was the most frequent severity category (38.3%), followed by mild (35.0%) and severe hyponatremia (26.7%). SIADH was the leading etiology, accounting for 25.8% of cases, followed by diuretic-induced hyponatremia (17.5%) and congestive heart failure (15.0%). Hypertension (49.2%) and diabetes mellitus (38.3%) were the most common associated comorbidities, while chronic kidney disease and heart failure were present in approximately 15% of patients each. (Table 2).

Table 2. Severity, Etiology and Associated Comorbidities (N=120)

The mean serum sodium concentration at presentation was 124.8 ± 5.6 mEq/L. The mean serum potassium level was 4.12 ± 0.74 mEq/L, while the mean blood urea and serum creatinine levels were 43.8 ± 20.7 mg/dL and 1.43 ± 0.81 mg/dL, respectively. The mean serum osmolality was 267.4 ± 14.8 mOsm/kg, and the average urine sodium concentration was 49.7 ± 26.5 mEq/L. (Table 3).

Table 3. Laboratory Characteristics of the Study Population (N=120)

Fluid restriction was the most commonly employed treatment modality (60.0%), followed by oral salt supplementation (45.0%) and normal saline infusion (40.0%). Hypertonic saline was administered to 30.0% of patients, whereas loop diuretics and tolvaptan were used in 18.3% and 14.2% of patients, respectively. Several patients received more than one therapeutic intervention according to the underlying etiology and severity of hyponatremia. (Table 4).

Table 4. Treatment Modalities Administered (N=120)

Clinical outcomes varied significantly according to the severity of hyponatremia. Patients with severe hyponatremia had the highest rates of ICU admission (53.1%), mechanical ventilation (37.5%), prolonged hospital stay (9.4 ± 3.8 days), and in-hospital mortality (25.0%). These outcomes were significantly worse compared with patients with mild and moderate hyponatremia (all p < 0.01). (Table 5).

Table 5. Clinical Outcomes According to Severity of Hyponatremia

Patients who did not survive were significantly older than survivors (71.3 ± 12.4 vs. 58.2 ± 15.8 years; p = 0.004) and had lower mean serum sodium levels at presentation (119.6 ± 4.2 vs. 125.4 ± 5.3 mEq/L; p < 0.001). Severe hyponatremia, chronic kidney disease, and congestive heart failure were significantly more common among non-survivors, indicating their association with increased in-hospital mortality. (Table 6).

Table 6. Factors Associated with In-Hospital Mortality

DISCUSSION

Hyponatremia is a common electrolyte abnormality among hospitalized adults and is particularly frequent in the elderly because of multiple comorbidities, polypharmacy, and impaired renal water handling. In the present study, the mean age was 59.8 ± 16.2 years, with nearly half of the patients being older than 60 years, and males constituted 56.7% of the study population. Generalized weakness was the predominant presenting symptom, followed by nausea/vomiting and altered sensorium. These findings are comparable with those reported by Singh et al., who also observed a higher prevalence of hyponatremia among older adults with neurological manifestations being the most frequent clinical presentation [13]. Similarly, epidemiological studies by Upadhyay et al. have shown that hyponatremia occurs predominantly in elderly hospitalized patients and is associated with substantial clinical burden [14].

In the present study, moderate hyponatremia was the most common severity category, while SIADH (25.8%) emerged as the leading etiology, followed by diuretic-induced hyponatremia and congestive heart failure. Hypertension and diabetes mellitus were the most frequent associated comorbidities. These observations are consistent with the review by Burst, which identified SIADH, diuretic therapy, heart failure, renal disease, and liver disease as the principal causes of hyponatremia in hospitalized adults [15]. In contrast, Singh et al. reported diuretic-induced hyponatremia as the most common etiology, followed by SIADH, highlighting the influence of differences in patient demographics, prescribing practices, and underlying disease patterns across institutions [13].

An important finding of the present study was the significant association between severe hyponatremia and adverse clinical outcomes. Patients with severe hyponatremia had significantly higher rates of ICU admission, mechanical ventilation, prolonged hospitalization, and in-hospital mortality compared with patients having mild or moderate hyponatremia. Furthermore, non-survivors were significantly older, had lower serum sodium concentrations, and more frequently had chronic kidney disease and congestive heart failure. These findings are in agreement with the large cohort study by Waikar et al., which demonstrated progressively increasing mortality with worsening hyponatremia among hospitalized patients [16]. Hoorn and Zietse also emphasized that hyponatremia is not only a marker of severe underlying illness but also an independent predictor of poor clinical outcomes and mortality, particularly in patients with cardiovascular, renal, and hepatic diseases [17].

Appropriate identification of the underlying etiology and timely institution of targeted therapy remain essential for improving outcomes in patients with hyponatremia. In the present study, fluid restriction was the most commonly employed treatment, followed by oral salt supplementation and isotonic saline, reflecting individualized management based on volume status and etiology. Current literature similarly recommends etiology-based treatment strategies, with fluid restriction being the cornerstone for SIADH and isotonic or hypertonic saline reserved for hypovolemic or symptomatic severe hyponatremia [15,18]. Overall, the findings of the present study reinforce existing evidence that early recognition of the underlying cause, careful correction of serum sodium, and prompt management of associated comorbidities are crucial in reducing morbidity and improving the prognosis of hospitalized adults with hyponatremia.

CONCLUSION

Hyponatremia is a common electrolyte disorder among hospitalized adults and is associated with diverse etiologies, with SIADH, diuretic use, and congestive heart failure being the most frequent causes in the present study. Increasing severity of hyponatremia was significantly associated with adverse clinical outcomes, including higher rates of intensive care unit admission, mechanical ventilation, prolonged hospital stay, and in-hospital mortality. Elderly patients and those with chronic kidney disease or heart failure were at particularly high risk of poor outcomes. Early identification of the underlying etiology, careful evaluation of contributing comorbidities, and prompt, etiology-specific management are essential to improve patient outcomes and reduce the morbidity and mortality associated with hyponatremia.

Acknowledgement: None

Funding: None

Conflict of Interest: None

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