Doctors perform the Allen test for many reasons. Primarily, the test is useful for examining the ulnar artery. Because the ulnar artery is not easily accessible from the skin’s surface, it is easier to examine it via comparison to the radial artery. The doctor must confirm that the hand will receive adequate blood flow without the radial artery. When it is blocked off, the hand receives blood only from the ulnar artery, which indicates the efficiency of the latter.

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