Hypocalcemia is a state of electrolyte imbalance in which the circulating serum calcium level is low. During hypocalcemia, the total calcium level and the ionized calcium level fall below the laboratory reference range.
Calcium is one of the most abundant electrolytes in the body, and levels are tightly controlled by parathyroid hormone and vitamin D. Calcium is essential for cell function, cell membrane stability, neuronal transmission, bone physiology, blood homeostasis, and cell signaling.
Circulating calcium levels are impaired by several factors, but hypocalcemia is mainly secondary to the imbalance of calcium absorption, excretion, and distribution.
As 40% of circulating calcium is bound to albumin, in a ratio of 1 mg albumin to 0.8 mg calcium, measuring albumin is essential in interpreting total serum calcium levels. However, if ionized calcium is determined, there is no need to measure albumin or adjust the value of calcium concentration. Approximately 15% of circulating calcium is bound to sulfates, phosphates, lactate, and citrate, and the remaining 45% circulates as biologically active calcium in an ionized form. 
Signs and symptoms
Hypocalcemia varies from a mild asymptomatic biochemical abnormality to a life-threatening disorder. Acute hypocalcemia can lead to paresthesia, tetany, and seizures (characteristic physical signs may be observed, including Chvostek sign, which is poorly sensitive and specific of hypocalcemia, and Trousseau sign).Image 3 Papilledema, cataracts, basal ganglia calcifications, and skin, hair, and dental changes may occur with chronic hypocalcemia. Neuropsychiatric manifestations include dementia in adults, anxiety, depression, lethargy, and extrapyramidal symptoms (parkinsonism). Skin exam may show dermatitis, eczema, hyperpigmentation, psoriasis, brittle hair with patchy alopecia, and brittle nails with characteristic transverse grooves. Image 2 Patients rarely may have congestive heart failure, angina, and hypotension.