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: Medicine
[{'content': 'The following are features of polycythemia rubra vera, except - \nSelect and explain. \nA. Increased red cell mass, B. Low aerial oxygen saturation, C. Presence of JAK2 mutation, D. Splenomegaly', 'role': 'user'}, {'content': 'Answer: B \nExplanation: <p>In PV, the major pathogenetic mechanism is a tyrosine kinase JAK2 mutation which removes the autoinhibitory control & activates the kinases.</p><p>Due to erythrocytosis, red cell mass will be increased .Splenomegaly produces abdominal fullness.But in PV, oxygen saturation will be high.</p><p>Reference :Harsh mohan textbook of pathology sixth edition pg no 359.</p>', 'role': 'assistant'}]