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For further information, see CMDT Part 21-07: Hypocalcemia

Key Features

Essentials of Diagnosis

  • Often mistaken as a neurologic disorder

  • 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

  • Increased excitation of nerve and muscle cells, primarily affects the neuromuscular and cardiovascular systems

  • Hypoalbuminemia is most common cause of low total serum calcium

  • When serum albumin concentration is < 4 g/dL (40 g/L), serum Ca2+ concentration is reduced by 0.8–1 mg/dL (0.20–0.25 mmol/L) for every 1 g/dL (10 g/L) of albumin

  • The most accurate measurement of serum calcium is the ionized calcium concentration

  • True hypocalcemia (decreased ionized calcium) implies insufficient action of PTH or active vitamin D

  • Important causes of hypocalcemia are listed in Table 21–6

  • The most common cause of hypocalcemia is advanced CKD

  • Magnesium depletion reduces both PTH release and tissue responsiveness to PTH, causing hypocalcemia

  • Hypocalcemia in pancreatitis is a marker of severe disease

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

Table 21–6.Causes of hypocalcemia.

Clinical Findings

Symptoms and Signs

  • 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 may appear

  • QT prolongation predisposes to ventricular arrhythmias

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 CKD, whereas it is suppressed in early CKD or vitamin D deficiency

  • Serum magnesium concentration is commonly low

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

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