This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Iron deficiency anemia, Subject name: Pathology
Earliest response to iron supplementation in iron deficiency anemia is denoted by? 
Select and explain. 
A. Increase in serum ferritin, B. Increase in reticulocyte count, C. Increase in iron binding capacity, D. Increase in hemoglobin
B: Increase in reticulocyte count
Answer: B: Increase in reticulocyte count 
Explanation: Response to iron therapy: Rapid subjective improvement, with disappearance or marked reduction of fatigue, lassitude, and other nonspecific symptoms, before any improvement in anemia is observed. Earliest hematologic evidence of response to treatment is an increase in reticulocytes on 5th to 10th day after sta of supplementation therapy & thereafter returns to normal. There is steady improvement in Hb and normalization of red cell indices. RETICULOCYTE IN BLUE LINE