A patient with chronic severe anaemia compensates remarkably well at rest despite a haemoglobin of 7 g/dL. Which change in his red cells best explains improved tissue oxygen delivery?

• A Increased intraerythrocytic 2,3-BPG shifting the dissociation curve to the left
• B Increased intraerythrocytic 2,3-BPG shifting the dissociation curve to the right ✓
• C Increased haemoglobin oxygen affinity secondary to reduced erythrocyte pH
• D Reduced intraerythrocytic 2,3-BPG prolonging red cell survival

Explanation

Chronic anaemia, hypoxia, and high altitude all raise red cell 2,3-BPG, which binds deoxygenated haemoglobin beta chains and stabilises the T state. This shifts the dissociation curve right, lowering affinity so more oxygen is unloaded at tissue PO2. Stored banked blood loses 2,3-BPG and therefore shows a LEFT shift after transfusion. Reduced pH would raise hydrogen ions and shift the curve right through the Bohr effect, not increase affinity.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.