Normal Ranges for Major Electrolytes
The normal ranges for major electrolytes in human plasma are: sodium 135-145 mEq/L, potassium 3.5-5.3 mEq/L, chloride 95-105 mEq/L, calcium 4.4-5.2 mEq/L (total calcium 8.8-10.4 mg/dL), magnesium 1.6-2.4 mEq/L, and phosphate 3-4.5 mg/dL. 1
Sodium (Na+)
- Normal range: 135-145 mEq/L
- Hyponatremia: <135 mEq/L
- Mild: 130-134 mEq/L
- Moderate: 125-129 mEq/L
- Severe: <125 mEq/L 2
- Hypernatremia: >145 mEq/L
- Clinical significance: Hyponatremia is the most common electrolyte abnormality in hospitalized patients, affecting approximately 15-30% of children and adults 1
Potassium (K+)
- Normal range: 3.5-5.3 mEq/L
- Hypokalemia: <3.5 mEq/L
- Mild: 3.0-3.5 mEq/L
- Moderate: 2.5-2.9 mEq/L
- Severe: <2.5 mEq/L 1
- Hyperkalemia: >5.3 mEq/L
- Mild: 5.5-6.4 mmol/L
- Moderate: 6.5-8.0 mmol/L
- Severe: >8.0 mmol/L 1
- Clinical significance: ECG changes typically don't appear until K+ <3.0 mEq/L (hypokalemia) or >6.5 mmol/L (hyperkalemia) 1
Chloride (Cl-)
- Normal range: 95-105 mEq/L
- Hypochloremia: <95 mEq/L
- Hyperchloremia: >105 mEq/L
- Clinical significance: Chloride abnormalities often parallel sodium abnormalities but can be independently associated with adverse outcomes in conditions like heart failure 3
Calcium (Ca2+)
- Normal range: 4.4-5.2 mEq/L (ionized calcium)
- Total calcium: 8.8-10.4 mg/dL (2.2-2.6 mmol/L)
- Hypocalcemia: <4.4 mEq/L (ionized) or <8.8 mg/dL (total)
- Hypercalcemia: >5.2 mEq/L (ionized) or >10.4 mg/dL (total)
- Clinical significance: Calcium plays a crucial role in neuromuscular function, cardiac contractility, and blood coagulation
Magnesium (Mg2+)
- Normal range: 1.6-2.4 mEq/L
- Hypomagnesemia: <1.6 mEq/L
- Hypermagnesemia: >2.4 mEq/L
- Clinical significance: Magnesium is essential for proper nerve and muscle function and serves as a cofactor in numerous enzymatic reactions
Phosphate (PO4)
- Normal range: 3-4.5 mg/dL (adults)
- Pediatric requirements: 47-70 mg/kg/day (parenteral), 60-140 mg/kg/day (enteral) 1
- Hypophosphatemia: <3 mg/dL
- Hyperphosphatemia: >4.5 mg/dL
- Clinical significance: Phosphate is critical for energy metabolism, bone mineralization, and acid-base balance
Bicarbonate (HCO3-)
- Normal range: 22-28 mEq/L
- Low bicarbonate: <22 mEq/L (metabolic acidosis)
- High bicarbonate: >28 mEq/L (metabolic alkalosis)
- Clinical significance: Key component of the body's buffer system for maintaining acid-base balance
Serum Osmolality
- Normal range: 275-295 mOsm/kg 1
- Calculation formula: 2 × Na (mEq/L) + BUN (mg/dL)/2.8 + glucose (mg/dL)/18 1
- Clinical significance: Important for assessing hydration status and evaluating causes of altered mental status
Clinical Considerations
Monitoring Recommendations
- Monitor electrolytes more frequently in:
Correction Principles
- Correct sodium abnormalities gradually to avoid osmotic demyelination syndrome
- Do not exceed correction rate of 3 mOsm/kg/h 4
- For severe hypokalemia with ECG changes, urgent replacement is required
- For severe hyperkalemia (>6.5 mmol/L), immediate treatment is necessary to prevent cardiac arrhythmias 1
Special Populations
- Pediatric patients may have different requirements:
- Sodium: 4-7 mEq/kg/day
- Potassium: 2-4 mEq/kg/day
- Calcium: 60-90 mg/kg/day (parenteral), 120-230 mg/kg/day (enteral)
- Magnesium: 4.3-7.2 mg/kg/day (parenteral), 7.9-15 mg/kg/day (enteral) 1
Electrolyte Abnormalities in Common Conditions
- DKA: Monitor for hypokalemia despite initially normal or elevated K+ levels due to insulin therapy 1, 4
- Heart failure: Increased risk of hyponatremia, hypokalemia, and hypochloremia 3
- Perinatal asphyxia: Severity correlates with degree of hyponatremia and hyperkalemia 5
Understanding these normal ranges and their clinical implications is essential for proper patient management and prevention of electrolyte-related complications.