This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Peripheral Arterial Occlusive Disease, Subject name: Surgery
For doing CABG , Allen&;s test is done to test which artery - 
Select and explain. 
A. Ulnar, B. Radial artery, C. Ant interosseous, D. Postinterosseous
A: Ulnar
Answer: A: Ulnar 
Explanation: Ans. is 'a' i.e.. Ulnar artery [Ref: Schwartz 9th/e p. 636; Sabiston 18th/e p. 1813; o Allen's test is used to assess collateral circulation in hand. In Allen's test, the radial artery is occluded by pressure over it at the wrist, for several minutes and the color of hand is compared with other hand. This is the first step and it indicates the presence of circulation through ulnar artery. In step 2, the ulnar artery is occluded similarly at wrist and colour compared with other hand and this gives an indication about circulation through radial artery. Since Radial artery is harvested for CABG as a conduit; patency of ulnar artery should be tested beforehand by Allen's test.