The modified Allen test differs mainly by examining both radial and ulnar arteries on the one hand and then repeated on the other side. Traditionally, it is performed by first having the patient arm flexed at the elbow with the fist clenched tightly or by asking the patient first to open and close their fist to help increase the draining of blood from the hands. The ulnar and radial arteries are then compressed by the provider’s thumbs simultaneously. The elbow is then extended to no more than 180 degrees, avoiding overextension as that could lead to a false positive test. The fist is then unclenched, and the palm should appear white. The compression is then released from the ulnar artery while maintaining pressure over the radial artery. Once the compression is released color should return to the palm usually within 10 seconds. The test is repeated on the same hand while releasing the radial artery first and continuing to compress the ulnar artery.