Which pulse site would the nurse use to perform the Allen test?

• A. Radial
• B. Ulnar
• C. Brachial
• D. Carotid

Answer: (B)

The Allen test is about checking collateral blood flow to the hand from the arteries at the wrist. It specifically assesses whether the ulnar artery can adequately perfuse the hand if the radial artery were blocked, which is why the test is performed at the wrist on the ulnar side. In practice, both the radial and ulnar arteries are occluded at the wrist, the hand is blanched, and then pressure on the ulnar artery is released to see if color returns quickly. A prompt return of color indicates good collateral circulation via the ulnar artery; poor or delayed return suggests limited collateral flow and potential risk if the radial artery were used for access.