Purpose: To assess the arterial blood flow to the hand.
Test Position: Sitting.
Performing the Test: The examiner palpates and applies pressure to the radial and ulnar arteries at the wrist, using three fingers on each artery. This occludes the blood flow to the hand. Have the patient make a tight fist and then open his/her hand 10 times, ending with the hand open. Hyperextension of the fingers and wrist should not occur as the tension in the soft tissues can appear white and lead to a false positive. The palm of the hand should then appear white/pale. The examiner then removes the pressure from one artery. A positive test occurs when it takes >5 seconds for color (blood) to return to the palm of the hand. Repeat the process, while removing pressure from the other artery, to assess the untested artery.
Importance of Test: This test is great at assessing blood flow, because when the pressure is applied to both arteries, blood is limited in its ability to enter the hand. With the repetitive opening and closing of the hand, the blood is pushed out of the hand, which explains it white/pale color. At the point where the tester removes pressure from one artery, the only pathway for blood to enter the hand becomes that artery, so any return of color (blood) to the hand signifies good blood flow in that artery.
Note: these tests should only be performed by properly trained health care practitioners.
References: Allen EV. "Thromboangiitis obliterans: methods of diagnosis of chronic occlusive arterial lesions distal to the wrist with illustrative cases." Am J Med Sci 1929; 178: 237-244.
Asif M, Sarkar PK. "Three-digit Allen's test." Ann Thorac Surg 2007 August; 84(2): 686-687.