This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Budd chiari syndrome & Pancreatitis, Subject name: Medicine
Most common cause of Budd-Chiari syndrome is: 
Select and explain. 
A. Hepatic vein valves, B. Hypercoagulable state in Nephrotic syndrome, C. PNH, D. Polycythemia vera
D: Polycythemia vera
Answer: D: Polycythemia vera 
Explanation: Primary Budd-Chiari syndrome (75%): thrombosis of the hepatic vein Secondary Budd-Chiari syndrome (25%): compression of the hepatic vein by an outside structure (e.g. a tumor) The cause for the disease cannot be found in about half of the patients. Hepatic vein thrombosis is associated with the following in decreasing order of frequency: Polycythemia vera": is a primary,absolute erythrocytosis. The EPO levels are suppressed causing alow to normal EPO in the blood. Pregnancy Post paum state Use of oral contraceptives Paroxysmal nocturnal hemoglobinuria Hepatocellular carcinoma Lupus anticoagulant