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Key Features

Essentials of Diagnosis

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

  • Frequently mistaken for a neurologic disorder

  • 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 active vitamin D3 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 21–7)

    • 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

Table 21–7.Causes of hypocalcemia.

Clinical Findings

Symptoms and Signs

  • Extensive spasm of skeletal muscle causes cramps and tetany

  • Laryngospasm with stridor can obstruct the airway

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

  • 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

  • In chronic hypoparathyroidism, cataracts and calcification of basal ganglia of the brain may occur

  • Ventricular arrhythmias if there is QT prolongation

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 in hypoparathyroidism or advanced stages of CKD, whereas it is suppressed in early-stages of CKD or vitamin D deficiency

  • Serum Mg2+ is commonly low

  • In respiratory alkalosis, total serum calcium is normal but ionized calcium is low

Diagnostic Procedure

  • ECG can ...

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