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Hypermagnesaemia CKD Mechanism — ESENeph MCQ

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EasyElectrolyte DisordersHypermagnesaemia CKD MechanismESENeph

A 55-year-old man with CKD G4 has a serum magnesium of 1.2 mmol/L (elevated, normal 0.7-1.0). He is on no magnesium supplements. What is the mechanism of hypermagnesaemia in CKD?

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Correct answer: E — Reduced renal magnesium excretion in advanced CKD causes mild hypermagnesaemia

The kidney is the primary regulator of magnesium balance, excreting 3-5% of filtered magnesium under normal conditions and up to 80% when intake is high. In CKD G4-5, reduced GFR impairs this compensatory excretion, leading to mild hypermagnesaemia (typically 1.0-1.3 mmol/L). This is usually asymptomatic. However, adding exogenous magnesium (Mg-containing antacids like Gaviscon Advance, laxatives like Milk of Magnesia, or supplements) can cause dangerous levels (>2 mmol/L) with neuromuscular and cardiac effects. BNF recommends avoiding Mg-containing products in severe CKD.

Reference: https://guidelines.ukkidney.org