Why does severe iron deficiency during erythropoiesis yield smaller red blood cells (microcytes) rather than normocytic cells in a patient with chronic kidney disease treated with recombinant erythropoietin?

💡 Explanation

Iron deficiency impairs heme synthesis, a necessary component of hemoglobin. Because EPO stimulates red blood cell production, a lack of iron constrains hemoglobin production within each cell, therefore resulting in smaller cells (microcytes) rather than normal-sized cells; this is because heme deficiency is rate-limiting rather than other causes.

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