The original Allen test can be performed by asking the patient to elevate both their hands above their head for thirty seconds. This will help with draining blood from the patient hands. Next, the patient is then asked to squeeze their hands into tight fists, and the radial artery is occluded simultaneously on both hands. The patient then open both hands rapidly, and the examiner will compare the color of both palms. The initial pallor should be replaced with the normal erythematous color of the hand as the blood from the collateral flow returns. The test is the repeated while occluding ulnar arteries instead of the radial arteries. The time it takes to the normal color to return helps indicate the degree of collateral blood flow. It is referred to as a negative test when there is a return of normal color to both hands during occlucion of either artery alone. A positive test will be when there is persistent pallor in palm indicating no collateral blood flow to the hand.