This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
A nine month old boy of Sindhi parents presented to you with complaints of progressive lethargy, irritability & pallor since 6 months of age. Examination revealed severe pallor. Investigation showed Hb-3.8 mg%; MCV-58 fl; MCH-19.4 pg/cell. Blood film shows osmotic fragility is normal (target cells and normoblasts). X-ray skull shows expansion of erythroid marrow. Which of the following is the most likely diagnosis? 
Select and explain. 
A. Iron deficiency anemia, B. Acute lymphoblastic anemia, C. Hemoglobin D disease, D. Hereditary spherocytosis
A: Iron deficiency anemia
Answer: A: Iron deficiency anemia 
Explanation: This child is having microcytic (MCV-58Fl), hypochromic(MCHC-19.4pg/cell) anemia with normal osmotic fragility. This is suggestive of iron deficiency anemia (Normal Hb at this age is 12g/dL, MCV is 78 fL). Severe iron deficiency will produce bizzare peripheral blood smear with severely hypochromic cells, target cells, hypochromic pencil shaped cells and occasionally small number of nucleated red blood cells. Ref: O P Ghai Essential Pediatrics, 6th Edition, Pages 300-302