What is the first step in performing the modified Allen test?

The first step in performing the modified Allen test involves having the patient clench their fist. This action helps to occlude the blood flow in the hand, particularly through the radial and ulnar arteries, promoting temporary paleness in the hand. This is crucial for observing the return of blood flow to the hand once the radial artery is released. By having the patient clench their fist, the clinician initiates the test conditions needed to assess the collateral circulation of the hand effectively. After the fist has been clenched and held, the clinician can then proceed with the subsequent steps, which include checking the capillary refill and blood flow once pressure is released from the radial artery.