In children with microcytic anemia, which laboratory finding suggests iron deficiency?

In children with microcytic anemia, an increased red cell distribution width (RDW) greater than 20% is a strong indicator of iron deficiency. RDW measures the variation in red blood cell size; when it is higher than normal, it suggests a mixed population of red blood cells—some that are small and some that may be normal or larger. This variability occurs in iron deficiency anemia because, as the body’s iron stores deplete, the bone marrow produces smaller red blood cells, leading to a greater difference in cell volume.

In contrast, a normal RDW can be seen in other types of microcytic anemia, such as thalassemia and anemia of chronic disease, where the red blood cell indices are less variable. Ferritin levels serve as a marker for iron stores in the body; high ferritin levels would indicate adequate iron storage, which contradicts the condition of iron deficiency. Low hemoglobin is a common finding in many types of anemia, but by itself, it does not specifically indicate iron deficiency.

Thus, the presence of a high RDW in a child with microcytic anemia is a reliable laboratory finding suggesting that the anemia is due to iron deficiency rather than another underlying cause.