This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Venous Disorders, Subject name: Surgery
Increase in D-dimer levels is noticed in immediate post-operative period. Most appropriate cause is: 
Select and explain. 
A. DVT, B. Pulmonary embolism, C. DIC, D. Normal
A: DVT
Answer: A: DVT 
Explanation: Post-operative period increases the risk of DVT due to immobilization. Diagnosis of DVT: D-dimer measurement: If normal, no indication for fuher investigation but, if raised, a duplex ultrasound examination of the deep veins should be performed Duplex ultrasound: Filling defects in flow and lack of compressibility indicate the presence of a thrombosis . Ascending venography: Shows thrombus as a filling defect, is now rarely required .