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: Medicine
Feature of hemorrhagic disease of new born is? 
Select and explain. 
A. Prolonged prothrombin time, B. Defective platelet count, C. Prolonged bleeding time, D. Prolonged thrombin time
A: Prolonged prothrombin time
Answer: A: Prolonged prothrombin time 
Explanation: Answer is A (Prolonged prothrombin time) Hemorrhagic disease of new born results from a deficiency of vitamin K. Prothrombin time is the single best laboratory test to detect vitamin K deficiency as vitamin k deficiency may present with isolated prolongation of PT Laboratory features of vitamin k deficiency (CMDT-2008) Both PT and PTT are prolonged but prolongation of PT is a more sensitive test to detect vitamin K deficiency than PTT - The PT is prolonged to a greater extent than PTT - With mild vitamin K deficiency only the PT is defective Fibrinogen level, Thrombin time and platlet count are not affected - CMDT