This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2017, Subject name: Pathology
A patient presented with headache and fever. His investigations revealed hemoglobin of 16g/dl, TLC of 21,000/ uL, platelet count of 3,75,000. His DLC showed Neutrophils (25%), Lymphocytes (20%), Metamyelocytes and myelocytes 40%and eosinophils5%. Which of the following is the next best investigation in this patient? 
Select and explain. 
A. JAK 2 mutation, B. EPO level, C. Philadelphia chromosome, D. Bone marrow biopsy
C: Philadelphia chromosome
Answer: C: Philadelphia chromosome 
Explanation: In the above question, lab investigation of the patient reveals normal hemoglobin, Elevated TLC, normal platelet count, decreased Neutrophils, Elevated metamyelocytes and myelocytes. This lab picture clearly indicates that immature WBC's are much more in number than the mature WBC'S. Such a condition is given the name "shift to the left". This is seen in association with two types of conditions: 1.) Leukemoid reaction 2.) CML To distinguish between the two condition, we can do: LAP score (not commonly performed now). - CML- decreased, Leukemoid reaction- increased. Philadelphia chromosome presence (confirmatory test)- CML- Philadelphia chromosome (+ve), Leukemoid reaction - Philadelphia chromosome(-ve) .