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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.

In a nutshell

Hypocalcaemia causes nerve and muscle hyperexcitability: paraesthesia, cramps, tetany, seizures and laryngospasm, with QT prolongation. Confirm the clinically relevant calcium, measure PTH/magnesium/phosphate/vitamin D/renal function, give monitored IV calcium for severe or symptomatic disease, and correct magnesium.

Classic presentation

A patient after total thyroidectomy develops perioral tingling and carpopedal spasm with a prolonged QT; think acute postoperative hypoparathyroidism and treat urgently.

Key points

  • Use albumin-adjusted or ionised calcium rather than total calcium alone.
  • Low or inappropriately normal PTH with high phosphate suggests hypoparathyroidism.
  • Hypomagnesaemia can make hypocalcaemia refractory to calcium.
  • Severe or symptomatic disease needs IV calcium gluconate with ECG monitoring.
  • Chronic hypoparathyroidism usually needs calcium plus active vitamin D and specialist monitoring.

First-line investigation

Adjusted or ionised calcium with ECG, PTH, magnesium, phosphate, vitamin-D status and renal function.

Management

Recognise the emergency

  • Escalate tetany, seizures, laryngospasm, significant QT prolongation/arrhythmia or markedly low calcium for urgent hospital treatment.1

Confirm and classify

  • Check adjusted or ionised calcium, ECG, PTH, magnesium, phosphate, vitamin-D status and renal function, then search for postoperative, renal, nutritional and acute-illness causes.1

Replace calcium safely

  • Give IV calcium gluconate with monitoring for severe/symptomatic disease; use oral calcium and vitamin-D replacement for stable chronic disease with current BNF checks.1,2

Correct magnesium and cause

  • Replace magnesium and address vitamin-D deficiency, hypoparathyroidism, CKD, malabsorption, pancreatitis, transfusion or other precipitant.1,2

Protect airway and heart

  • Use senior critical-care/airway and cardiology support for laryngospasm, seizures, ventricular arrhythmia or persistent symptoms despite calcium.1

Avoid overcorrection

  • Monitor calcium, magnesium, phosphate and renal function during treatment and follow chronic hypoparathyroidism for hypercalciuria and renal complications.1,2

Exam traps

  • A low total calcium with low albumin may be pseudohypocalcaemia.
  • Alkalosis lowers ionised calcium and can cause tetany even when total calcium is normal.
  • Correct magnesium when calcium will not respond.
  • Low PTH with high phosphate is hypoparathyroidism; high PTH is a secondary response unless magnesium is suppressing it.
  • Calcium replacement without follow-up can cause hypercalciuria and renal complications.

Illustrations

Carpopedal spasm in Trousseau's signA recreated positive Trousseau posture showing carpopedal spasm with wrist and metacarpophalangeal flexion and extension of the fingers in latent hypocalcaemic tetany.Tmdswan, Wikimedia Commons · CC-BY-SA-4.0

Key sources

  1. Society for Endocrinology: emergency management of acute hypocalcaemia in adult patients (UK endocrine emergency guidance for assessment and initial treatment of acute hypocalcaemia; published September 2016 with a 2019 dose addendum and accessed 4 August 2026.)
  2. British National Formulary (BNF) (Current UK prescribing information for calcium salts, alfacalcidol, calcitriol, magnesium and vitamin-D preparations; product-specific dose, infusion and monitoring details must be checked at the point of care; accessed 4 August 2026.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.