Endocrinology & Metabolic

Hypocalcaemia

Hypocalcaemia is low biologically available serum calcium, usually from hypoparathyroidism, vitamin-D deficiency, chronic kidney disease or hypomagnesaemia; rapid or symptomatic hypocalcaemia causes tetany, seizures, laryngospasm and QT prolongation and requires urgent treatment.

Definition

Hypocalcaemia is low serum calcium after accounting for albumin, or low ionised calcium. It may be acute or chronic; rapid or symptomatic hypocalcaemia and disease with tetany, seizures, laryngospasm, QT prolongation or arrhythmia is an emergency.

First principles

Low extracellular calcium makes excitable tissue unstable

Extracellular calcium normally raises the threshold for opening voltage-gated sodium channels. When ionised calcium falls, nerves and muscles depolarise more readily, producing perioral or digital paraesthesia, cramps, carpopedal spasm, tetany, seizures and sometimes laryngospasm. Cardiac repolarisation is prolonged, so the QT interval lengthens and arrhythmia risk rises.

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