Mild Hypernatremia Definition
Mild hypernatremia is defined as a serum sodium level of 146-149 mmol/L. 1, 2
Severity Classification of Hypernatremia
Hypernatremia severity is stratified based on serum sodium concentration:
- Mild hypernatremia: 146-149 mmol/L 2
- Moderate hypernatremia: 150-169 mmol/L 2
- Severe (threatening) hypernatremia: ≥170 mmol/L 2
The baseline threshold for hypernatremia is serum sodium >145 mmol/L. 1, 2, 3
Clinical Context and Symptoms
Patients with mild hypernatremia often present with nonspecific neurologic symptoms. The most common presentations include somnolence (42% of cases), disorientation (30%), and recent falls (17%). 4, 5 These symptoms occur due to cellular dehydration affecting the central nervous system. 2
The occurrence and severity of symptoms correlate with the absolute elevation of serum sodium rather than the rate of change in mild cases. 4 However, even at the mild severity range (146-149 mmol/L), neurologic manifestations can be present and should not be dismissed. 5
Common Etiologies in Mild Hypernatremia
The primary cause is impaired thirst mechanism or lack of access to water, accounting for approximately 70% of cases. 5 This is particularly common in elderly patients, those with cognitive impairment, or hospitalized individuals with restricted mobility. 1, 5
Other contributing factors include dehydration from extrarenal losses (gastrointestinal, insensible losses) and, less commonly in the mild range, diabetes insipidus. 1, 2
Critical Management Considerations
A common pitfall is inadequate initial correction—approximately 35% of patients experience either correction <2 mmol/L or paradoxical worsening during the first 24 hours. 5 This inadequate treatment is associated with significantly higher mortality. 5
For mild hypernatremia that has developed chronically (over days), correction should not exceed 0.4 mmol/L per hour to prevent cerebral edema from rapid osmotic shifts. 2 Treatment focuses on addressing the underlying cause and providing hypotonic fluid replacement when indicated. 1