Hypocalcaemia is a state of electrolyte imbalance in which the circulating serum calcium level is low. During hypocalcaemia, the total calcium level and the ionised 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 signalling.
Circulating calcium levels are impaired by several factors, but hypocalcaemia 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 ionised 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 ionised form. 
Signs and symptoms
Hypocalcaemia varies from a mild asymptomatic biochemical abnormality to a life-threatening disorder. Acute hypocalcaemia can lead to paraesthesia, tetany, and seizures (characteristic physical signs may be observed, including Chvostek's sign, which is poorly sensitive and specific of hypocalcaemia, and Trousseau's sign).View image Papilloedema, cataracts, basal ganglia calcifications, and skin, hair, and dental changes may occur with chronic hypocalcaemia. Neuropsychiatric manifestations include dementia in adults, anxiety, depression, lethargy, and extrapyramidal symptoms (parkinsonism). Skin examination may show dermatitis, eczema, hyperpigmentation, psoriasis, brittle hair with patchy alopecia, and brittle nails with characteristic transverse grooves.View image Patients rarely may have congestive heart failure, angina, and hypotension.
- Isolated hypoparathyroidism
- Autoimmune hypoparathyroidism
- HIV-related hypoparathyroidism
- Renal failure
- Acute pancreatitis
- Extensive osteoblastic skeletal metastasis
- Hungry bone syndrome
- Drug-induced hypocalcaemia
- Multiple transfusions
- Drug interference with assay
- Infiltrative hypoparathyroidism
- DiGeorge syndrome and other developmental complexes
- Tumour lysis syndrome
- Constitutively activating calcium sensing receptor (CaSR) abnormalities (mutations or autoimmune activation)
- Vitamin D resistance or receptor mutations