This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
The difference between leukemia and leukemoid reaction is done by - 
Select and explain. 
A. Leukocyte alkaline phosphatase, B. Immature cells, C. Total leukocyte count, D. E.S.R.
A: Leukocyte alkaline phosphatase
Answer: A: Leukocyte alkaline phosphatase 
Explanation: Leukemoid reaction is defined as a reactive excessive leukocytosis in peripheral blood resembling that of leukemia in a subject who doesnot have leukemia. Leucocyte alkaline phosphatase (LAP) score in the cytoplasm of mature neutrophils is high in leukaemoid reaction whereas reduced in CML .It is very useful to distinguish between the two. Reference; Harsh Mohan textbook of pathology, 7th edition.Pg no.332