Sodium
Overview
Sodium measures serum concentration of this major extracellular cation essential for maintaining osmotic pressure, fluid balance, nerve impulse transmission, and muscle contraction. It is primarily regulated by renal excretion under aldosterone and antidiuretic hormone control. Hyponatremia (low sodium) may indicate SIADH, heart failure, diuretics, or water intoxication, while hypernatremia (high sodium) suggests dehydration, diabetes insipidus, or salt loading; it is clinically useful for guiding fluid therapy, diagnosing electrolyte disorders, and monitoring hospitalized patients at risk for osmotic demyelination or cerebral edema.Clinical Use Cases
- Diagnosing and managing hyponatremia in hospitalized patients.
- Evaluating hypernatremia from dehydration or diabetes insipidus.
- Monitoring fluid status in heart failure, cirrhosis, or renal disease.
- Guiding correction rates to prevent osmotic demyelination syndrome.
- Assessing SIADH versus cerebral salt wasting.
Specimen Types
- Serum.
- Plasma.
- Whole blood (point-of-care).
Measurement Methods
- Ion-selective electrode (ISE, primary method).
- Indirect potentiometry (automated analyzers).
- Direct potentiometry (blood gas analyzers).
Test Preparation and Influencing Factors
- No fasting required.
- Avoid prolonged tourniquet application (causes hemoconcentration).
- Pseudohyponatremia from hyperlipidemia or hyperproteinemia (indirect ISE).
- Recent IV fluid administration or hyperglycemia affects levels.
- Collect anaerobically for accurate point-of-care results.
Synonyms
- Serum sodium.
- Na+.
- Natrium.