Normal Blood Sodium Levels in Healthy Adults
The normal blood sodium level in a healthy adult is 135-145 mEq/L (or mmol/L), with values below 135 mEq/L defined as hyponatremia and values above 145 mEq/L defined as hypernatremia. 1, 2, 3
Standard Reference Range
- Serum sodium concentration of 135-145 mmol/L represents the accepted normal range for healthy adults, derived from healthy population studies 2, 3, 4
- This range is consistent across major clinical guidelines and laboratory standards 1, 2
Important Clinical Context
Age and Population Variations
- The standard reference range (135-145 mmol/L) is derived from healthy populations and may not fully apply to hospitalized patients 4
- Hospitalized patients, particularly those over 65 years, tend to have lower sodium levels than outpatients of the same age, with a broader distribution of values 4
- Emergency admissions show significantly lower sodium levels compared to elective admissions 4
Clinical Significance of "Normal" Values
- Even values at the higher end of the normal range (>139-140 mmol/L) in hospitalized patients are associated with increased mortality risk 4
- Among inpatients, mortality risk begins rising at 140 mmol/L, well within the traditionally "normal" range, with patients at 145 mmol/L having 3.7 times higher risk of in-hospital death compared to those at 140 mmol/L 4
- Mild deviations from normal (130-134 mmol/L for hyponatremia or 145-150 mmol/L for hypernatremia) carry significant clinical implications, including increased hospital stay and mortality 5, 2
Abnormal Sodium Levels
Hyponatremia classification: 1, 2, 3
- Mild: 130-135 mmol/L (or 126-135 mmol/L in some classifications)
- Moderate: 120-129 mmol/L (or 120-125 mmol/L)
- Severe: <120 mmol/L
Hypernatremia classification: 5
- Mild: 145-150 mmol/L
- Severe: >150 mmol/L
Prevalence of Abnormalities
- Hyponatremia affects approximately 5% of adults in the general population and 35% of hospitalized patients, making it the most common electrolyte disorder 2, 3
- Hypernatremia is less common, occurring in approximately 3% of hospitalized patients 5, 6
Mortality Associations
- Both hyponatremia and hypernatremia on admission are associated with significantly increased short- and long-term mortality 5, 6
- Hypernatremia carries higher mortality risk than hyponatremia, with severe hypernatremia (>150 mmol/L) associated with 52% in-hospital mortality compared to 14% with severe hyponatremia (<125 mmol/L) 5
- Even mild chronic hyponatremia (130-135 mmol/L) is associated with cognitive impairment, gait disturbances, increased falls (23.8% vs 16.4% in normonatremic patients), and fractures (23.3% vs 17.3% over 7.4 years) 2