Oxygen transport in a woman with hemoglobin Hope/β⁺ thalassemia

Because their blood may 'unload' oxygen more readily than normal, people with hemoglobin of low oxygen affinity might be expected to be anemic. We have studied a woman with hemoglobin Hope/β⁺ thalassemia, whose hemoglobin level was 10.4 to 12.3 gm/dl (normal 14 ± 2) despite a P₅₀ of 41 mm Hg (normal 26). Her cardiac index was normal yielding a calculated mixed venous PO₂ of 51 mm Hg (normal 34 to 49). Oxygen transport in patients with low oxygen affinity can be maintained by a variety of homeostatic responses, only one of which is altered erythropoiesis.