This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vascular surgery, Subject name: Surgery
Aeriovenous fistula can safely be ligated if the following is positive: 
Select and explain. 
A. Allen's Test, B. Henle-Coenen sign, C. Tredelenberg test, D. Schwaz Test
A: Allen's Test
Answer: A: Allen's Test 
Explanation: Allen&;s Test: Tests the adequacy of the blood supply to the hand from the radial and ulnar aeries and the arcade between them. Allen&;s test is used to know the integrity of palmar arch (Patency of radial and ulnar aeries). If these are patent, AVF can be safely ligated. Method of Allen&;s Test Elevate the hand and apply digital pressure on the radial and ulnar aeries occlude them. Ask the patient to make a fist several times. The tips of the finger should go pale. Release each aery in turn and observe the return of colour. Ref: Sabiston 20th edition Pgno: 1979