Hypocalcemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
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Overview
Hypocalcemia is the presence of low serum calcium levels in the blood, usually taken as less than 3.5 mmol/L or 8.8 mg/dl or an ionized calcium level of less than 1.1 mmol/L (4.5 mg/dL). It is a type of electrolyte disturbance. In the blood, about half of all calcium is bound to proteins such as serum albumin, but it is the unbound, or ionized, calcium that the body regulates. If a person has abnormal levels of blood proteins then the plasma calcium may be inaccurate. The ionized calcium level is considered more clinically accurate in this case.
Calcium is the most abundant mineral in the body. 99% of the body's calcium is stored in bone. Calcium is found in plasma and is either protein-bound or ionized and readily available.
Historical Perspective
The association between thyroid and parathyroid surgery and hypocalcemia was made by Billroth, Kocher, Mayo, and Halsted.
Classification
There is a functional classification of hypocalcemia which includes complete absent of PTH gland, PTH insufficiency, and PTH overactivity.
Pathophysiology
Hypocalcemia may develop in disorders associated with insufficient parathyroid hormone or vitamin D production or resistance to hormonal activities. Perturbations of calcium homeostasis can be caused by environmental factors or occur as a result of genetic mutations in the calcium-sensing receptor (as in type 1 autosomal dominant hypocalcemia), Gs α subunit (as in type 1A and 1B pseudohypoparathyroidism), vitamin D hydroxylase (as in type 1 vitamin D-dependent rickets , and calcitriol receptor (as in type 2 vitamin D-dependent rickets).