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
The earliest indicator of response after staing iron in a 6 year old girl with iron deficiency is: 
Select and explain. 
A. Increased reticulocyte count, B. Increased hemoglobin, C. Increased ferritin, D. Increased serum iron
A: Increased reticulocyte count
Answer: A: Increased reticulocyte count 
Explanation: Following iron therapy in a child with iron deficiency anemia, initial bone marrow response is seen within 48hours. The earliest response seen is a rise in the level of reticulocyte which occur by the 2nd to 3rd day. This is followed by elevation of hemoglobin level. After the correction of the hemoglobin levels, body iron stores are repleted. Ref: Essential Pediatrics, 6th Edition By O P Ghai, Page 302.