Which statement best describes the CBC pattern consistent with iron deficiency anemia in a toddler?

Which statement best describes the CBC pattern consistent with iron deficiency anemia in a toddler?

• A. Low MCV and low RDW
• B. Low MCV and elevated RDW
• C. High MCV and elevated RDW
• D. Normal MCV and RDW

Answer: (B)

Iron deficiency anemia in toddlers typically shows small red blood cells with more variation in their size. A low MCV means the average red cell is smaller than normal, and an elevated RDW means there is a wide range of cell sizes (anisocytosis). This pattern occurs because as iron stores become depleted, newer red cells are progressively smaller, while some cells are still larger or earlier formed, creating a mix of sizes. This combination—low MCV with high RDW—is most consistent with iron deficiency. In contrast, conditions like thalassemia trait often have a low MCV but a normal or only mildly elevated RDW, since the red cells are uniformly small. A high MCV would point toward macrocytic processes (not typical for iron deficiency), and normal MCV and RDW would not reflect iron-deficiency–driven changes.

Iron deficiency anemia in toddlers typically shows small red blood cells with more variation in their size. A low MCV means the average red cell is smaller than normal, and an elevated RDW means there is a wide range of cell sizes (anisocytosis). This pattern occurs because as iron stores become depleted, newer red cells are progressively smaller, while some cells are still larger or earlier formed, creating a mix of sizes.

This combination—low MCV with high RDW—is most consistent with iron deficiency. In contrast, conditions like thalassemia trait often have a low MCV but a normal or only mildly elevated RDW, since the red cells are uniformly small. A high MCV would point toward macrocytic processes (not typical for iron deficiency), and normal MCV and RDW would not reflect iron-deficiency–driven changes.