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Calcium Homeostasis & Disturbances

🧪 Calcium Homeostasis & Disturbances

Hypercalcaemia and hypocalcaemia — causes, clinical features, ECG changes, and management. Two metabolic emergencies you must distinguish at a glance.

At a Glance

Calcium disturbances are high-yield topics in MRCS, particularly the ECG changes (directly tested in MCQs), the causes by clinical context (outpatient vs inpatient), and the specific clinical signs of hypocalcaemia. Nail the comparison below and the rest builds naturally.

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Hypercalcaemia
Ca²⁺ > 2.6 mmol/L (corrected)
HIGH CALCIUM
Top Cause1° Hyperparathyroidism (outpatient) / Malignancy (inpatient)
SymptomsStones, Bones, Groans, Psychic Moans
ECG⚡ Shortened QT interval
ManagementIV 0.9% saline → bisphosphonates
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Hypocalcaemia
Ca²⁺ < 2.1 mmol/L (corrected)
LOW CALCIUM
Top CausePost-thyroid/parathyroid surgery; massive blood transfusion
SignsTrousseau’s, Chvostek’s, stridor, perioral paraesthesia
ECG⚡ Prolonged QT interval
ManagementIV 10% Calcium Gluconate
Calcium Disturbances — Quick Reference Normal Ca²⁺: 2.2–2.6 mmol/L HYPERCALCAEMIA Ca²⁺ > 2.6 mmol/L PRIMARY CAUSE 1° Hyperparathyroidism (outpatient setting) 2nd CAUSE Malignancy (inpatient setting) Stones · Bones · Groans · Psychic Moans 🪨 Renal stones 🦴 Bone pain / osteitis fibrosa cystica 🤢 Constipation / vomiting / abdo pain 🧠 Confusion / depression / psychosis ECG: SHORTENED QT interval Ca²⁺ shortens ventricular repolarisation — plateau phase compressed Rx: IV 0.9% Saline → Bisphosphonates Force calciuresis first · IV pamidronate / zoledronate to reduce bone resorption HYPOCALCAEMIA Ca²⁺ < 2.1 mmol/L SURGICAL CAUSE Post-thyroid / parathyroid Parathyroid glands damaged TRANSFUSION CAUSE Massive blood transfusion Citrate chelates Ca²⁺ Clinical Signs of Tetany 💊 Perioral paraesthesia (earliest) 💪 Trousseau’s sign (BP cuff → carpal spasm) 👋 Chvostek’s sign (tap facial nerve → twitch) 🌬️ Stridor (laryngeal tetany — life-threatening) ECG: PROLONGED QT interval Ca²⁺ prolongs ventricular repolarisation → risk of torsades de pointes Rx: IV 10% Calcium Gluconate 10 mL of 10% Ca gluconate IV over 10 min · repeat as needed · monitor ECG

The Exam Priority

Three things that are directly tested: (1) ECG changes — shortened QT in hypercalcaemia, prolonged QT in hypocalcaemia; (2) context of cause — outpatient vs inpatient hypercalcaemia; (3) clinical signs of hypocalcaemia — Trousseau’s, Chvostek’s, stridor. Know all three cold.

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