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
One year old baby exclusively breast fed has a 1cm. hepatomegaly severe pallor and no spleen.The most important investigation is – 
Select and explain. 
A. B12 estimation, B. Serum iron estimation, C. Folic and estimation, D. Fetal hemoglobin estimation
B: Serum iron estimation
Answer: B: Serum iron estimation 
Explanation: By the age of 6 months the breast-fed infant's diet should be supplemented with iron fortified complementary foods because iron in breast milk is sufficient upto the age of 6 months.
The baby in question has been exclusively breast fed upto 1 year, so he has developed iron deficiency anemia.