The blood supply to your hand normally comes from two arteries: the radial artery and the ulnar artery. A procedure called the Allen test can be used to find out if blood flow to your hand is normal. This test checks to see if both of these blood vessels are open and working correctly. It may be done before a blood draw, before a procedure that involves one of the arteries, or to help check for a blood flow problem.
How It Is Done
For the Allen test, you will likely rest your hand on a table or towel and make a fist. The health professional will apply pressure to the arteries in your wrist for several seconds. You may be asked to open and close your hand a few times. The pressure will stop the blood flow to your hand, and your hand will become cool and pale. Blood is then allowed to flow through one of the arteries. The health professional will see if your hand becomes warm and returns to its normal color. The test may be done again to check blood flow in the other artery.
Your hand quickly becomes warm and returns to its normal color. This means that the artery that was checked is enough to supply blood to your hand and fingers.
Your hand remains pale and cold. This means that the artery that was checked cannot supply enough blood to your hand and fingers.