Iron Deficiency Anemia in Infancy

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A 9-month-old boy born at term is brought because of pallor and increasing irritability. He remains exclusively breastfed, and no iron-fortified cereal, pureed meat, or legumes have been introduced. Examination shows pale conjunctivae and palmar creases. Hemoglobin is 8.0 g/dL, mean corpuscular volume 60 fL, red cell distribution width 18 %, reticulocyte count 1 %, and platelets 520 × 10⁹/L. What is the most likely cause of his anemia?

  1. A.Vitamin B12 deficiency
  2. B.Beta thalassemia trait
  3. C.Iron deficiency anemiaCorrect
  4. D.Sickle cell anemia

Explanation

This infant has a microcytic hypochromic anemia with a high red cell distribution width, a low reticulocyte count, and reactive thrombocytosis, which is the textbook laboratory signature of iron deficiency. The clinical context seals the diagnosis: prolonged exclusive breastfeeding beyond 6 months without complementary iron-rich foods or supplementation exhausts the hepatic iron stores laid down in the third trimester, and 9 months is the classic age of presentation. Breast milk iron is highly bioavailable but present in very small quantities, so it cannot meet the requirements of rapid growth after about 6 months of age. Confirmatory iron studies would show a low serum ferritin, low serum iron, high total iron binding capacity, and low transferrin saturation, and treatment is oral elemental iron 3 to 6 mg/kg/day with dietary counselling. Beta thalassemia trait also produces microcytosis but characteristically with a disproportionately low mean corpuscular volume relative to a mild anemia, a normal or low red cell distribution width, a high red cell count, and a raised hemoglobin A2 on electrophoresis. Vitamin B12 deficiency causes a macrocytic anemia with hypersegmented neutrophils and neurologic regression, typically in infants of strictly vegan or B12-deficient mothers. Sickle cell anemia presents with a normocytic hemolytic anemia, a high reticulocyte count, jaundice, and vaso-occlusive pain or dactylitis rather than an isolated hypoproliferative microcytic picture. Iron deficiency in this age group also carries a risk of lasting neurodevelopmental impairment, which is why prompt recognition and treatment matter.

Why each option

A.
Vitamin B12 deficiency causes macrocytic anemia with hypersegmented neutrophils and neurologic features, not microcytosis.
B.
Beta thalassemia trait gives microcytosis out of proportion to a mild anemia with a normal red cell distribution width and a raised hemoglobin A2.
C.
Correct. Prolonged exclusive breastfeeding without complementary iron, microcytic hypochromic indices, high red cell distribution width, low reticulocytes, and thrombocytosis all point to iron deficiency.
D.
Sickle cell anemia is a normocytic hemolytic anemia with reticulocytosis and jaundice, and it rarely presents before 6 months because of protective hemoglobin F.

Reference: Nelson Textbook of Pediatrics, 22nd ed., 2024, Iron Deficiency Anemia

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