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
First, change of improves weft noted after iron therapy is initiated – 
Select and explain. 
A. Decreased irritability, B. Reticulcytosis, C. Increase in serum iron levels, D. Replenishment of iron stores
A: Decreased irritability
Answer: A: Decreased irritability 
Explanation: "When specific iron therapy is given, patients often show rapid subjective improvement, with the disappearance or marked diminution of fatigue, lassitude, and other nonspecific symptoms (e.g. irritability). This response may occur before any improvement in anemia observed" Wintrobe's

The earliest haematological evidence of response of treatment is an increase in the percentage of reticulocytes and their hemoglobin content.

So,

Overall earliest indicator of improvement → decreased fatigue, lassitude and other nonspecific symptoms
Earliest haematological evidence of improvement → Increased reticulocyte count.