Description

• 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.

Etiology

• 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, 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.

• 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