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Fetal haemoglobin oxygen affinity — MRCPCH TAS MCQ

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EasyPhysiologyFetal haemoglobin oxygen affinityMRCPCH TAS

A term infant has a higher oxygen affinity haemoglobin pattern than an older child. The oxygen dissociation curve is shifted to the left. What is the most likely explanation?

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Correct answer: B — Reduced binding of 2,3-BPG to fetal haemoglobin

Fetal haemoglobin binds 2,3-BPG less avidly than adult haemoglobin, increasing oxygen affinity and shifting the curve left. Increased beta-chain production would move the haemoglobin profile towards adult haemoglobin. This allows transfer of oxygen from maternal to fetal blood across the placenta.

Reference: Ganong's Review of Medical Physiology; Nelson Textbook of Pediatrics; RCPCH Theory examination syllabi