• Hypocalcemia is defined as a total plasma calcium level <8.7 mg/dL:
    • Ionized calcium may be normal and, therefore, have no clinical manifestations
  • Normal total serum calcium concentrations are 8.7–10.5 mg/dL
  • Normal ionized calcium levels are 4.64–5.28 mg/dL


  • Incidence in the general population is 0.6%
  • Mechanism:
    • From either increased loss of calcium from the circulation or decreased entry into the circulation
    • Intravascular calcium circulates in 3 forms:
      • Bound to proteins (mainly albumin): 45–50%
      • Bound to complexing ions (citrate, phosphate, carbonate): 5–10%
      • Ionized (free) calcium (physiologically active form): 45–50%
    • Serum levels of calcium are primarily controlled by 3 hormones:
      • Parathyroid hormone (PTH)
      • Decrease in calcium levels leads to an increase in PTH secretion (increasing bone resorption, renal absorption, intestinal absorption, and urinary phosphate excretion)
    • Vitamin D (1,25-dihydroxyvitamin D):
      • Decrease in calcium level activates vitamin D (increasing bone resorption and intestinal absorption)
    • Calcitonin:
      • Causes a direct inhibition of bone resorption with increased calcium levels
  • Hypoalbuminemia – the most common cause:
    • Each 1 g/dL decrease in serum albumin decreases protein-bound serum calcium by 0.8 mg/dL
    • Ionized (free) calcium levels do not change

Pediatric Considerations
  • Children have higher values of normal calcium (9.2–11 mg/dL)
  • Neonatal hypocalcemia: Total serum calcium concentrations <7.5 mg/dL or serum-ionized calcium levels <4 mg/dL
  • Symptoms of hypocalcemia in infancy:
    • Hyperactivity, jitteriness
    • Tachypnea
    • Apneic spells with cyanosis
    • Vomiting

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