Electrolytes
Electrolytes
Electrolytes are minerals that carry an electrical charge when dissolved in body fluids. They are essential for maintaining fluid balance, nerve conduction, muscle contraction, cardiac rhythm, acid–base balance, and cellular function.
Major Electrolytes
| Electrolyte | Main functions | Normal serum range* |
|---|---|---|
| Sodium (Na⁺) | Fluid balance, nerve function | 135–145 mEq/L |
| Potassium (K⁺) | Cardiac rhythm, muscle & nerve function | 3.5–5.0 mEq/L |
| Chloride (Cl⁻) | Fluid balance, acid–base balance | 98–106 mEq/L |
| Bicarbonate (HCO₃⁻) | Acid–base regulation | 22–29 mEq/L |
| Calcium (Ca²⁺) | Bone, muscle contraction, coagulation | 8.5–10.5 mg/dL |
| Magnesium (Mg²⁺) | Neuromuscular function, enzyme activity | 1.7–2.4 mg/dL |
| Phosphate (PO₄³⁻) | ATP production, bone, cellular metabolism | 2.5–4.5 mg/dL |
*Reference ranges can vary slightly between laboratories.
Why Electrolytes Matter
1. Sodium
- Main extracellular cation.
- Regulates extracellular fluid volume and osmolality.
- Abnormalities can cause confusion, seizures and altered consciousness.
2. Potassium
- Critical for myocardial electrical activity.
- Hyperkalemia can produce life-threatening arrhythmias.
- Hypokalemia may cause weakness, cramps and ventricular arrhythmias.
3. Calcium
- Important for myocardial and skeletal muscle contraction.
- Essential for coagulation and bone mineralization.
- Low calcium can cause tetany, paresthesias and QT prolongation.
4. Magnesium
- Supports potassium and calcium homeostasis.
- Hypomagnesemia may contribute to refractory hypokalemia and ventricular arrhythmias, including torsades de pointes.
5. Bicarbonate
- A major component of the body’s buffering system.
- Helps assess metabolic acidosis and alkalosis.
Common Causes of Electrolyte Imbalance
- Vomiting or diarrhea
- Excessive sweating
- Dehydration
- Kidney disease
- Heart failure
- Endocrine disorders
- Diuretic therapy
- Certain antihypertensive medications
- Excessive or inadequate fluid intake
- Severe infections and critical illness
Symptoms
Electrolyte abnormalities may cause:
Fatigue • weakness • muscle cramps • nausea • headache • confusion • dizziness • palpitations • seizures • abnormal heart rhythms
Severe abnormalities—particularly involving potassium, sodium, calcium or magnesium—can be medical emergencies.
Key Clinical Point
In a patient with arrhythmia, weakness, altered mental status, dehydration, or significant gastrointestinal losses, checking electrolytes is often an important part of the initial evaluation. Interpretation should consider renal function, medications, acid–base status, ECG findings and the clinical context, rather than relying on an isolated laboratory value.
