When performing the Allen test, which artery is released first?

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

Answer: (A)

The key idea is evaluating collateral blood flow to the hand through the palmar arches before using a specific artery for a procedure. In the Allen test, you first occlude both the radial and ulnar arteries to blanch the hand. Releasing the artery that you want to test for its ability to supply the hand by itself shows whether there is adequate collateral circulation.

Releasing the ulnar artery first is the best choice because it directly tests whether the ulnar pathway can restore perfusion through the palmar arch. If color returns quickly after releasing the ulnar, it indicates the ulnar artery (and the palmar arch it supplies) can adequately perfuse the hand, meaning it’s safe to proceed with using the radial artery for cannulation or procedures. If perfusion doesn’t return, the hand would rely too much on the radial artery, posing a risk if the radial artery were compromised.

The other arteries listed aren’t the ones this test primarily evaluates in this sequence: the brachial and femoral arteries aren’t part of the hand’s palmar circulation assessed by this test, and the radial artery is typically the one evaluated for potential cannulation after confirming adequate collateral flow via the ulnar artery.