Hypocalcemia pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Overview

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), G_s 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).

Pathophysiology

Physiology

The normal physiology of Hypocalcemia can be understood as follows:

• The normal concentrations of calcium in the body is maintained within the narrow range and that is required for the minimal activity of the many extra- and intracellular processes calcium regulates. 
• Calcium transport within the blood is mainly bound to plasma proteins like albumin (45%),phosphate and citrate(15%) and ionized state(40%).
• Only the ionized form of calcium is active but most laboratories shows report of total serum calcium concentrations.
• The normal concentration of calcium ranges between 8.5 and 10.5 mg/dL.
• The normal range of ionized calcium in the plasma is 4.65 to 5.25 mg/dL.

Pathogenesis

• It is understood that Hypocalcemia is the result caused by the following

Hypoalbuminemia:

• When there is a fluctuate in the protein concentrations especially albumin,total calcium levels may change.
• whereas the level of ionized calcium remains relatively stable, because it is hormonally regulated.
• So that the total serum calcium levels may not accurately reflect the physiologically important ionized calcium concentration.

Alkalosis

In alkalosis, hydrogen ions dissociate from the negatively charged albumin, which allows for increased calcium binding and leads to a decreased concentration of free calcium.

For an increase in pH of 0.1 unit, there is an approximately 0.05 mmol/L (0.1 mEq/L) fall in the serum level of ionized calcium.

Respiratory Alkalosis

Reduced ionized calcium concentration and hypocapnia associated with hyperventilation may contribute to symptoms of vasoconstriction including lightheadedness, fainting, and parasthesia.

Globulin Binding

Calcium binding to globulin is relatively small (1.0 g of globulin binds 0.2–0.3 mg of calcium) and generally does not influence the total serum calcium concentration.

References