Refractory Hypocalcaemia — RACP Adult Medicine MCQ

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ModerateGeneral Internal MedicineRefractory HypocalcaemiaRACP Adult Medicine

A 45-year-old man presents with progressive weakness over 2 days, areflexia, and perioral numbness. His calcium is 0.95 mmol/L (critically low) and magnesium is 0.3 mmol/L. Despite IV calcium replacement, his calcium remains refractory. What must be corrected to enable calcium correction?

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Correct answer: E — Magnesium

Hypomagnesaemia causes refractory hypocalcaemia through two mechanisms: (1) impaired PTH secretion (magnesium is required for PTH release) and (2) end-organ resistance to PTH in bone and kidney. Correcting magnesium is essential before calcium can be normalised. IV magnesium sulphate (2–4 g over 20 minutes, then infusion) should be administered. Common causes include GI losses, diuretics, PPI use, alcohol, and aminoglycosides.

Reference: eTG – 2025 – Endocrinology; AMH – 2025 – Electrolyte Disorders