Serum Sodium


  • Sodium is the most abundant cation and the chief base of the blood.
  • Its primary functions in the body are to maintain osmotic pressure and acid-base balance chemically and to transmit nerve impulses.
  • Mechanisms for maintaining a constant sodium level in the plasma and extracellular fluid include renal blood flow, carbonic anhydrase enzyme activity, aldosterone, and action of other steroids.
  • Determinations of serum sodium balance detect changes in water balance rather than sodium balance.
  • Sodium levels are used to determine electrolytes, acid-base balance, water balance, water intoxication and dehydration.
Normal Values
  • Infants: 133 – 142 mEq/L
  • Children (1 – 16 years old): 136 – 145 mEq/L
  • Adults: 136 – 145 mEq/L
  • This is done by obtaining 5 mL of venous blood serum sample.
  • Heparinized blood can be used.
  • Avoid hemolysis.
Clinical Implications
  • Increased sodium / hypernatremia:
    1. dehydration and insufficient water intake
    2. Conn’s syndrome
    3. primary aldosteronism
    4. coma
    5. Cushing’s disease
    6. diabetes insipidus
    7. tracheobronchitis
  • Decreased sodium / hyponatremia:
    1. severe burns
    2. congestive heart failure
    3. excessive fluid loss such as severe diarrhea, vomiting
    4. excessive IV induction of nonelectrolyte fluids such as glucose
    5. Addison’s disease
    6. severe nephritis
    7. pyloric obstruction
    8. malabsorption syndrome
    9. diabetic acidosis
    10. drugs such as diuretics
    11. edema
    12. large amounts of water per orem
    13. hypothyroidism
    14. excessive ADH production
Interfering Factors
  • Anabolic steroids, corticosteroids, calcium, fluorides, and iron can increase sodium levels.
  • Heparin, laxatives, sulfates and diuretics can cause decreases in sodium levels.
  • High triglycerides or low protein can cause artificially low sodium values.
Decreased serum sodium
  1. Assess for signs and symptoms of hyponatremia. (apprehension, anxiety, muscular, twitching, muscular weakness, headaches, tachycardia and hypotension)
  2. Be knowledgeable that hyponatremia after surgery is the result of SIADH. There is an increased reabsorption from the kidney and sodium dilution between one to two days before the surgery.
  3. Take vital signs to determine cardiac status during hyponatremia.
Increased serum sodium
  1. Check for signs and symptoms of hypernatremia. (restlessness, thirst, flushed skin, sticky mucous membrane, a rough dry tongue and tachycardia)
  2. Keep an accurate record of input and output of fluids.
  3. Observe for signs of edema and overhydration resulting from an elevated serum sodium level.