Calcium is vital for life, and extracellular
calcium concentrations must constantly be maintained within a precise concentration range. Low serum
calcium (
hypocalcemia) occurs in conjunction with multiple disorders and can be life-threatening if severe. Symptoms of acute
hypocalcemia include neuromuscular irritability,
tetany, and
seizures, which are rapidly resolved with
intravenous administration of
calcium gluconate. However, disorders that lead to chronic
hypocalcemia often have more subtle manifestations.
Hypoparathyroidism, characterized by impaired secretion of
parathyroid hormone (PTH), a key regulatory
hormone for maintaining
calcium homeostasis, is a classic cause of chronic
hypocalcemia. Disorders that disrupt the metabolism of
vitamin D can also lead to chronic
hypocalcemia, as
vitamin D is responsible for increasing the gut absorption of
dietary calcium. Treatment and management options for chronic
hypocalcemia vary depending on the underlying disorder. For example, in patients with
hypoparathyroidism,
calcium and
vitamin D supplementation must be carefully titrated to avoid symptoms of
hypocalcemia while keeping serum
calcium in the low-normal range to minimize
hypercalciuria, which can lead to renal dysfunction. Management of chronic
hypocalcemia requires knowledge of the factors that influence the complex regulatory axes of
calcium homeostasis in a given disorder. This chapter discusses common and rare disorders of
hypocalcemia, symptoms and workup, and management options including replacement of PTH in
hypoparathyroidism.