Hypocalcemia

Calcium is vital for many important bodily functions like nerve transmission, bone structure, signaling between cells, and blood coagulation. Most of the body's calcium is stored in bones, although some of it circulates in the blood. About 40% of the calcium in blood is bound to proteins in blood, mainly albumin. Protein-bound calcium acts as a reserve of calcium for the cells but has no active role in the body. Only unbound calcium influences the body’s functions. Unbound calcium has an electrical (ionic) charge, so it is also known as ionized calcium. Thus, hypocalcemia causes complications only when the level of ionized calcium is low. 

Hypocalcemia or low levels of calcium occurs when a total serum calcium concentration is < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4.7 mg/dL (< 1.17 mmol/L).

Calcium levels are regulated by hormones like a parathyroid hormone (PTH), Vitamin D, and calcitonin. Hypocalcemia is most commonly a consequence of Vitamin D inadequacy or hypoparathyroidism, or a resistance to these hormones and it has also been associated with many drugs as well.

Hypocalcemia can range from being asymptomatic in mild cases to life-threatening in acute cases. Manifestations include paresthesias, tetany, and, when severe, seizures, encephalopathy, and heart failure.

Diagnosis of hypocalcemia involves measurement of serum calcium with adjustment for serum albumin concentration. Treatment is administration of calcium, sometimes along with Vitamin D.