Hypocalcemia

Key Features

Essentials of Diagnosis

• Serum calcium concentration is low (< 8.5 mg/dL or < 2.21 mmol/L)

• Usually asymptomatic, but can cause cramps or tetany if severe

• Check for decreased serum parathyroid hormone (PTH), vitamin D, or magnesium levels

• Despite a low total serum calcium, calcium metabolism is likely normal if ionized calcium level is normal

General Considerations

• The most common cause of low total serum calcium is hypoalbuminemia

• The most common cause of hypocalcemia is advanced chronic kidney disease (CKD), in which decreased production of calcitriol and hyperphosphatemia both play a role

• Elderly hospitalized patients with hypocalcemia and hypophosphatemia, with or without an elevated serum PTH level, are likely deficient in vitamin D

• There is increased excitation of nerve and muscle cells, primarily affecting the neuromuscular and cardiovascular systems

Etiology

• Decreased intake or absorption (Table 21–6)

  • Malabsorption

  • Small bowel bypass

  • Vitamin D deficit, including 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D

• Increased loss

  • Alcoholism

  • CKD

  • Diuretic therapy

• Endocrine disease

  • Hypoparathyroidism

  • Sepsis

  • Pseudohypoparathyroidism

  • Calcitonin secretion from medullary carcinoma of the thyroid

  • Familial hypocalcemia

• Physiologic causes

  • Decreased serum albumin but normal ionized calcium

  • Decreased end-organ response to vitamin D

  • Hyperphosphatemia

  • Loop diuretics

Clinical Findings

Symptoms and Signs

• Tetany from increased neuromuscular irritability

  • Hallmark sign of severe hypocalcemia (ionized calcium < 1 mmol/L)

  • Generally uncommon with higher ionized calcium levels

• Laryngospasm with stridor can obstruct the airway

• Convulsions, paresthesias of lips and extremities, and abdominal pain

• Less pronounced symptoms include fatigue, anxiety, and depression

• Chvostek sign (contraction of the facial muscle in response to tapping the facial nerve)

• Trousseau sign (carpal spasm occurring after occlusion of the brachial artery by a blood pressure cuff) is usually readily elicited

• Ventricular arrhythmias if there is QT prolongation, though serious dysrhythmias are rare

Diagnosis

Laboratory Tests

• Serum calcium concentration is low (< 8.5 mg/dL or < 2.21 mmol/L)

• In true hypocalcemia, the ionized serum calcium concentration is low (< 4.6 mg/dL or < 1.15 mmol/L)

• Serum phosphate is usually elevated ...