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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Common causes: vitamin D deficiency (most common UK cause), hypoparathyroidism (post-surgical), CKD, hypomagnesaemia, acute pancreatitis
- Clinical: perioral/digital paraesthesiae, tetany, Chvostek sign, Trousseau sign, seizures, prolonged QT on ECG
- Always check magnesium — hypomagnesaemia prevents PTH secretion and must be corrected first
- Acute/severe: IV calcium gluconate 10% — 10 mL over 10 min with cardiac monitoring. Can repeat/infuse
- Chronic: oral calcium + vitamin D (colecalciferol for deficiency; alfacalcidol/calcitriol if PTH-dependent activation impaired)
- ECG: prolonged QT interval → risk of Torsades de Pointes. Continuous monitoring in acute setting
Overview
Hypocalcaemia is defined as an albumin-adjusted serum calcium below the normal range (<2.2 mmol/L). Symptoms arise from increased neuromuscular excitability due to calcium's role in stabilising neuronal membranes. The severity of symptoms depends more on the rate of fall than the absolute level. Causes are classified by PTH status: low PTH (hypoparathyroidism — post-surgical, autoimmune, congenital), high PTH (vitamin D deficiency, CKD, pseudohypoparathyroidism), and functional (hypomagnesaemia, acute pancreatitis, massive blood transfusion with citrate, tumour lysis syndrome, rhabdomyolysis). Vitamin D deficiency is the commonest cause in the UK community setting.
Epidemiology
Hypocalcaemia is a common electrolyte disturbance, particularly in hospitalised patients (up to 18% of ICU patients). Vitamin D deficiency is extremely prevalent in the UK — estimated to affect 1 in 5 adults. Groups at highest risk: elderly, housebound, dark-skinned individuals, those wearing covering clothing, malabsorption (coeliac, Crohn's), CKD patients, and neonates. Post-surgical hypocalcaemia occurs in up to 30% of total thyroidectomy patients (usually transient). Chronic hypoparathyroidism prevalence is approximately 20–40 per 100,000.
Clinical Features
Symptoms
Perioral paraesthesiae (tingling around mouth)
Digital paraesthesiae (tingling in fingers and toes)
Muscle cramps and spasms
Tetany and carpopedal spasm
Seizures (generalised tonic-clonic)
Laryngospasm and stridor
Anxiety, irritability, confusion
Signs
Chvostek sign: tap over facial nerve → ipsilateral facial twitch (sensitive but not specific)
Trousseau sign: inflate BP cuff >systolic for 3 min → carpopedal spasm (main d'accoucheur) — more specific
Prolonged QT interval on ECG
Hypotension (severe hypocalcaemia impairs cardiac contractility)
Papilloedema (chronic, rare)
Investigations
First-line
Albumin-adjusted calcium<2.2 mmol/L. Always correct for albumin — low albumin gives falsely low total calcium
PTHLow = hypoparathyroidism. High = secondary causes (vitamin D deficiency, CKD, pseudohypoparathyroidism)
MagnesiumLow Mg impairs PTH secretion and action — MUST correct before calcium will normalise
ECGProlonged QT interval. Continuous monitoring if symptomatic
Second-line
Vitamin D (25-OH)Low in deficiency (<25 nmol/L = deficient). Most common cause of hypocalcaemia in UK
PhosphateLow + low Ca²⁺ = vitamin D deficiency. High + low Ca²⁺ = hypoparathyroidism or CKD
U&Es, eGFRCKD is a common cause (impaired 1-alpha hydroxylation of vitamin D)
ALPElevated in vitamin D deficiency (secondary hyperparathyroidism causes increased bone turnover → osteomalacia)
Specialist
Ionised calciumMore accurate than total calcium in critically ill patients — not affected by albumin. Available on ABG
1
Acute/severe hypocalcaemia
- IV calcium gluconate 10%: 10 mL (2.2 mmol Ca²⁺) IV over 10 min with continuous cardiac monitoring
- Repeat bolus if symptoms persist. Then: IV infusion 40 mL 10% calcium gluconate in 1 L 0.9% NaCl over 8–12 h
- Check and replace magnesium: IV MgSO₄ 8 mmol (2 g) over 15 min if low
- Do NOT use calcium chloride peripherally — tissue necrosis risk. Use gluconate
- Monitor ECG and calcium levels 6-hourly during infusion
2
Chronic/mild hypocalcaemia
- Vitamin D deficiency: colecalciferol (vitamin D3) loading then maintenance (NICE recommends 800–4000 IU/day)
- Hypoparathyroidism: alfacalcidol or calcitriol + oral calcium (see hypoparathyroidism entry)
- CKD: alfacalcidol/calcitriol (active vitamin D — kidneys cannot 1-alpha hydroxylate)
- Oral calcium supplements: calcium carbonate 500 mg–1.5 g daily
Complications
- Cardiac arrest: Severe hypocalcaemia can cause QT prolongation → Torsades de Pointes → cardiac arrest
- Seizures: Generalised tonic-clonic from neuronal hyperexcitability
- Laryngospasm: Life-threatening airway obstruction
- Chronic: Cataracts, basal ganglia calcification, dental enamel defects, osteomalacia/rickets
UKMLA Exam Tips
- 1Always correct calcium for albumin. Low albumin = falsely low total calcium. Ionised calcium is the true physiological value
- 2Vitamin D deficiency = low Ca²⁺ + low phosphate + HIGH PTH + high ALP. Hypoparathyroidism = low Ca²⁺ + HIGH phosphate + LOW PTH
- 3Hypomagnesaemia must be corrected BEFORE calcium will normalise — Mg is required for PTH secretion
- 4IV calcium gluconate is safe peripherally. Calcium chloride needs a central line
- 5Massive blood transfusion → hypocalcaemia from citrate chelation. Check calcium after >4 units
- 6Post-thyroidectomy: hypocalcaemia from damage to parathyroids. Check calcium within 24 hours
practicetest your knowledge on hypocalcaemiaApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — endocrine and beyond.
open q-bank