Modified Allen Test ABG Nursing Assessment before collecting an arterial blood gas from the radial artery. The modified Allen test is used by nurses, respiratory therapists, and other healthcare professionals to determine whether there is good collateral blood flow to the hand in case there is a complication during ABG collection. In this video, you can see a quick demonstration of how to perform the modified allen test, as well as a simple nursing mnemonic to help you remember the steps.