Red blооd cells regulаte оxygen delivery by modulаting 2,3‐bisphosphoglycerаte (2,3‐BPG) levels via the Rapoport–Luebering shunt. Under chronic hypoxic conditions, 2,3‐BPG levels increase, thereby reducing hemoglobin’s oxygen affinity to promote oxygen release in tissues. Which of the following pathological conditions is most characteristically associated with an upregulation of 2,3‐BPG levels in red blood cells?