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Source: Pai, AB. Disorders of Calcium and Phosphorus Homeostasis. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. Accessed August 20, 2012.

  • Total serum calcium <8.5 mg/dL (<2.13 mmol/L) with ionized calcium <4.4 mg/dL (<1.1 mmol/L)

  • Primary causes:
    • Postoperative hypoparathyroidism secondary to surgical procedures involving thyroid, parathyroid, and neck.
    • Vitamin D deficiency
  • Other causes:
    • Magnesium deficiency
    • Medications
      • Drug-induced hypocalcemia:
        • Furosemide
        • Calcitonin
        • Bisphosphonates
        • Oral phosphorus agents
      • Drug-induced hypomagnesemia
        • Aminoglycosides
        • Diuretics
        • Cisplatin
    • Hypoalbuminemia
    • Chronic kidney disease

  • Vitamin D necessary for optimal absorption of calcium and phosphorus
    • Deficiency most common cause of chronic hypocalcemia worldwide.
  • Hypomagnesemia impairs parathyroid hormone (PTH) secretion and induces resistance of target organs to PTH actions.
    • Associated with severe symptomatic hypocalcemia unresponsive to calcium replacement therapy.
    • Calcium normalization dependent on magnesium replacement.

  • Infrequent in outpatient setting
    • Most common in elderly, malnourished patients and as result of sodium phosphate bowel preparation agents.
  • Higher incidence in intensive care unit patients

  • Maintain adequate vitamin D intake.

  • Vitamin D deficiency associated with:
    • Gastrointestinal disease including:
      • Gastric surgery
      • Chronic pancreatitis
      • Small-bowel disease
  • Malnutrition
  • Use of drugs known to induce hypocalcemia or hypomagnesemia (see Etiology)

  • Clinical manifestations are variable and depend on onset of hypocalcemia.

Signs and Symptoms

  • Acute decrease in serum calcium
    • Tetany: hallmark sign manifested as:
      • Neuromuscular irritability with increased seizure potential and:
        • Paresthesia around mouth and in extremities
        • Muscle spasms and cramps
        • Hand and feet spasms
    • Cardiovascular
      • Electrocardiogram (ECG) changes include prolonged QT interval
      • Arrhythmias
      • Bradycardia
  • Chronic hypocalcemia
    • Depression
    • Anxiety
    • Memory loss
    • Confusion

Means of Confirmation and Diagnosis

  • Total serum calcium <8.5 mg/dL (<2.13 mmol/L) with ionized calcium <4.4 mg/dL (<1.1 mmol/L)

Laboratory Tests

  • Metabolic panel
    • Serum calcium
      • Corrected total serum calcium calculated as follows:
        • Corrected Sca (mg/dL) = measured Sca (mg/dL) + [0.8 x (40 g/dL – measured albumin (g/dL))] or Corrected Sca (mmol/dL) = measured Sca (mmol/dL) + [0.02 x (40 g/L – measured albumin (g/L))]
    • Serum albumin
    • Serum magnesium
    • Serum phosphorus

Diagnostic Procedures

  • ECG

Differential Diagnosis

  • Resolution of signs and symptoms
  • Restoration of normocalcemia
  • Management of associated electrolyte abnormalities
  • Treatment of underlying cause

  • Emergent treatment rarely warranted unless life-threatening symptoms present (e.g., frank tetany or seizures).

  • Acute, symptomatic hypocalcemia requires IV administration of soluble calcium salts (Figure 1).
    • Initially, 100–300 mg of elemental calcium (e.g., 1 g calciumchloride, 2–3 g calcium gluconate) should be given IV over 5–10 minutes (≤60 mg of elemental calcium per minute).
      • Effective for only 1–2 hours
      • Follow bolus dose with continuous infusion of elemental calcium (0.52 mg/kg/hour) usually for 2–4 hours and then maintenance dose (0.30.5 mg/kg/hour).
  • Correct underlying cause and other electrolyte problems after acute hypocalcemia corrected.
    • Magnesium supplementation indicated ...

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