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Citrate hypocalcaemia during massive transfusion — FRCA Primary MCQ

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HardPhysiologyCitrate hypocalcaemia during massive transfusionFRCA Primary

A patient has massive transfusion during trauma laparotomy. Ionised calcium falls, blood pressure drops and coagulation worsens. Which component of transfused blood products most directly explains the hypocalcaemia?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Citrate anticoagulant binding ionised calcium

Citrate in stored blood products chelates ionised calcium, and rapid transfusion can exceed hepatic citrate metabolism, causing hypocalcaemia. Potassium may rise during transfusion but does not explain ionised calcium binding. Reduced 2,3-DPG affects oxygen unloading rather than calcium. The clinical pearl is to monitor and replace ionised calcium during massive transfusion.

Reference: RCoA Primary FRCA Syllabus 2026; Ganong's Review of Medical Physiology; West's Respiratory Physiology