In a 5‑month‑old girl with failure to thrive, pallor, hepatosplenomegaly, severe microcytic anemia and modest reticulocytosis, which diagnosis is most likely: beta‑thalassemia, hemoglobin C disease, hemoglobin H disease, or iron deficiency?

Beta-Thalassemia Major

In this 5-month-old infant with severe microcytic anemia (hemoglobin 4 g/dL, MCV 68 fL), failure to thrive, hepatosplenomegaly, and a modest reticulocyte response (3%), the most likely diagnosis is beta-thalassemia major. The combination of extreme anemia presenting in early infancy with organomegaly and inadequate reticulocyte response despite severe anemia points definitively to a hemoglobinopathy rather than nutritional deficiency.

Key Diagnostic Features Supporting Beta-Thalassemia

Age of presentation is the critical discriminator. Beta-thalassemia major manifests in early infancy (typically before 2 years of age) as fetal hemoglobin declines and the defective beta-globin chains become clinically apparent 1, 2. Iron deficiency would be extremely unusual at 5 months in a breastfed or formula-fed infant without significant blood loss 3.

The reticulocyte count of 3% is inappropriately low for the severity of anemia. With a hemoglobin of 4 g/dL, the bone marrow should mount a vigorous reticulocytosis (typically >10-15%) if iron or substrate were available 3. This blunted response reflects ineffective erythropoiesis characteristic of beta-thalassemia, where defective red cell precursors undergo intramedullary hemolysis 1, 2.

Hepatosplenomegaly at this age strongly favors thalassemia. Extramedullary hematopoiesis and hemolysis drive organ enlargement in beta-thalassemia major, whereas iron deficiency rarely causes significant organomegaly in infants 1, 2.

The RDW of 16% does not exclude thalassemia in this context. While classic teaching suggests RDW ≤14% favors thalassemia trait over iron deficiency 3, 4, approximately 50% of thalassemia cases can show elevated RDW 3. In beta-thalassemia major with severe anemia and ineffective erythropoiesis, the RDW is frequently elevated 5, 6.

Why Other Diagnoses Are Less Likely

Iron deficiency is improbable because:

• The age of presentation is too early for dietary iron deficiency in a developed country 3
• Hepatosplenomegaly is not a feature of uncomplicated iron deficiency in infants 3
• The reticulocyte response is inadequate; iron deficiency typically shows reticulocytosis once anemia becomes severe 3
• Failure to thrive from iron deficiency alone would require months of severe depletion 3

Hemoglobin H disease (alpha-thalassemia with 3-gene deletion) presents with chronic hemolytic anemia and splenomegaly but typically causes milder anemia (hemoglobin 7-10 g/dL) and would show a more robust reticulocyte response (5-10%) due to ongoing hemolysis 2, 5.

Hemoglobin C disease is a mild hemoglobinopathy that does not cause severe anemia or failure to thrive in infancy 7. Homozygous Hb C disease produces mild hemolytic anemia with hemoglobin typically 9-12 g/dL 7.

Confirmatory Testing Required

Hemoglobin electrophoresis or HPLC is the definitive diagnostic test and will reveal absent or markedly reduced hemoglobin A, elevated hemoglobin F (often >70%), and elevated hemoglobin A2 in beta-thalassemia major 8, 1, 5. This test should be performed immediately 8, 5.

Serum ferritin and transferrin saturation should be measured to confirm that iron stores are normal or elevated (ferritin typically >30 μg/L), excluding concurrent iron deficiency 8, 1. Beta-thalassemia patients often have normal or elevated ferritin due to ineffective erythropoiesis and increased intestinal iron absorption 1, 2.

Genetic testing will identify the specific beta-globin gene mutations and is required for family counseling and prenatal diagnosis in future pregnancies 1, 5.

Immediate Management Priorities

Urgent packed red blood cell transfusion is required to correct life-threatening anemia (hemoglobin 4 g/dL) and prevent high-output cardiac failure 1, 2. Beta-thalassemia major requires lifelong regular transfusions starting in early childhood to maintain hemoglobin >9-10 g/dL 1, 2.

Referral to a pediatric hematologist for comprehensive thalassemia care is mandatory, including transfusion protocols, iron chelation therapy (which will be needed after repeated transfusions), growth monitoring, and consideration for hematopoietic stem cell transplantation—the only curative option 8, 1, 2.

Avoid iron supplementation unless true iron deficiency is documented with low ferritin (<30 μg/L), as inappropriate iron therapy in thalassemia leads to dangerous iron overload 8, 1.

Critical Pitfall to Avoid

Do not assume microcytic anemia in infancy is iron deficiency and initiate empiric iron therapy without hemoglobin electrophoresis. In a 5-month-old with severe anemia, failure to thrive, and hepatosplenomegaly, hemoglobinopathy screening is the first diagnostic step 8, 1, 5. Delaying this diagnosis prevents timely transfusion therapy and allows progression of skeletal deformities, growth failure, and cardiac complications from chronic severe anemia 1, 2.