What is the purpose of performing the modified Allen test?

The modified Allen test is specifically designed to assess the integrity of collateral circulation in the hand, particularly before performing procedures like arterial puncture. By temporarily occluding the radial and ulnar arteries, this test evaluates whether blood supply via the ulnar artery is adequate to sustain the hand if the radial artery is punctured. The significance lies in ensuring that there is sufficient blood flow to the hand through collateral channels, which is crucial for patient safety during procedures that involve the arteries.

This assessment confirms that the ulnar artery can sufficiently supply blood to the hand if damage to the radial artery occurs, thereby minimizing the risk of ischemia or complications related to arterial access. The ability to visualize the return of color and normal function to the hand after releasing pressure indicates that collateral circulation is intact, supporting the procedure's safety. This reason emphasizes the importance of confirming collateral circulation as a protective measure in phlebotomy practices involving arterial access.