Diagnosis: Thalassemia Major
The diagnosis is C - Thalassemia major, based on the combination of severe microcytic anemia (low MCV, low Hb), nucleated red blood cells, target cells on peripheral blood smear, and critically, a normal/low RDW of 6. This constellation of findings is pathognomonic for thalassemia rather than iron deficiency anemia.
Key Diagnostic Features Supporting Thalassemia
The RDW of 6 (which is abnormally low/normal) is the most discriminating feature - a low MCV with RDW ≤14.0% strongly suggests thalassemia minor or major, while a low MCV with RDW >14.0% suggests iron deficiency anemia 1, 2.
Nucleated red blood cells (NRBCs) on peripheral smear indicate severe hemolysis and ineffective erythropoiesis, which is characteristic of thalassemia major but not typically seen in iron deficiency anemia 3.
Target cells are a hallmark finding in thalassemia due to the imbalanced globin chain synthesis and abnormal red cell membrane configuration 3, 4.
The combination of severe microcytosis with relatively uniform red cell size (low RDW) distinguishes thalassemia from IDA, where iron deficiency produces a heterogeneous population of red cells with elevated RDW 1, 3.
Why Other Options Are Incorrect
Iron deficiency anemia (Option B) is ruled out because IDA characteristically shows elevated RDW (>14.0%), and the presence of nucleated RBCs and target cells is atypical for simple iron deficiency 1, 2, 3.
Lead poisoning (Option D) can cause microcytic anemia with basophilic stippling, but the RDW pattern and clinical presentation described are more consistent with thalassemia 4.
Hereditary schistocytes (Option A) would show fragmented red cells (schistocytes) rather than target cells and nucleated RBCs, and is associated with microangiopathic hemolytic processes 5.
Clinical Context and Confirmation
Pallor and lethargy are consistent with severe anemia from thalassemia major, where chronic hemolysis and ineffective erythropoiesis lead to profound anemia requiring regular transfusions 6.
Confirmatory testing should include hemoglobin electrophoresis to identify the specific globin chain abnormality (elevated HbF and HbA2 in beta-thalassemia major) 1, 4.
In thalassemia major, MCV is disproportionately low relative to the degree of anemia, often with MCV <70 fL, which helps distinguish it from other microcytic anemias 7, 3.