Allen Test

Historical Overview

• 1929: Edgar V. Allen (1900–1961) described a test for evaluating arterial blood flow to the hands. The patient is instructed to make tight fists with both hands for one minute to squeeze the blood out of them. The examiner then compresses either the radial or ulnar artery of each hand. During compression of either artery, the flow through the uncompressed artery is evaluated by checking the return of color to the hand and fingers when the patient is told to extend their fingers rapidly.¹
• 1952: Irving S. Wright (1901–1997) suggested a modification whereby one hand is examined at a time. The patient is instructed to elevate one hand and clench their fist firmly. The examiner then simultaneously compresses both the radial and the ulnar arteries of that hand. The patient is then instructed to lower and open the hand in a relaxed fashion so as not to overextend it, and the examiner then releases the pressure over one of the arteries, and checks for the return of color to the hand.¹

Description

• The Allen test is used for suspected arterial occlusion. If a patient's hand flushes fully and rapidly after an artery is released, that artery, the palmar arch, and the digital arteries are patent. If pallor persists throughout the hand, the artery that was released is occluded. Pallor in patches indicates insufficiency of the smaller vessels.¹

Pathophysiology

• Arterial occlusion

Instructions²

• The patient is asked to raise and clench the hand to squeeze blood out of the cutaneous vascular bed
• The examiner compresses the radial artery in the radial groove and the ulnary artery at the proximal end of Guyon’s canal
• The patient opens their hand without hyperextending the fingers
• The examiner then releases compression of one artery and notes the time taken for the palm to recover to normal color
• The maneuver is then repeated to test the second artery in the same hand.
• The maneuver is then repeated to test the arteries in the opposite hand.

Variations^3-5

• The time used to determine when the hand has returned to normal color is variable. This can take from 3−15 seconds in individuals without occlusion.
• Using a pulse oximeter on the thumb may increase the objectivity of the test and make it less dependent on patient cooperation.
• The arteries are compressed with three digits, and the patient asked to open and clench their hand 10 times.

Related Signs and Tests²

• Pulse oximetry added to the modified Allen test
• Incorporating plethysmography in the modified Allen test
• “Snuff Box” test
• “Squirt” test
• Postocclusive reactive circulatory hyperaemia test
• Measurement of the systolic thumb pressure
• Radial hyperemic response test
• Doppler ultrasound
• MRI

Diagnostic Performance Characteristics*

• Individuals who have a positive (NORMAL) test result have adequate ulnar and radial perfusion of the hand, and the color of their hand returns to normal, typically within 6 seconds after the hand is relaxed and arterial compression is released.

• A negative Allen test suggests that the artery being tested does not adequately supply blood to the hand. It strongly suggests an arterial occlusion.

• Modified Allen test is most commonly used in clinical practice.
• Typical arterial compression time is 6 seconds.
• It may take up to 15 seconds for the normal color to return in some individuals, even if no occlusion is present.
• There is wide variability among examiners. In one study, 4 clinicians examined 200 hands, and there was not a single case in which all 4 examiners agreed.
• False positives can occur due to hyperextension of the wrist or metacarpophalangeal joints, and false negatives can occur due to incomplete compression of the radial artery.
• An American Academy of Orthopaedic Surgeons (AAOS) clinical practice guideline concluded that the Allen test is useful in ruling out other conditions in cases of suspected carpal tunnel syndrome.¹⁰
• Any abnormalities suggested by an abnormal (NEGATIVE) Allen test should be immediately verified by a Doppler study.
• References 3,10,11

1. Ejrup B, Fischer B, Wright IS. Clinical evaluation of blood flow to the hand: the false-positive Allen Test. Circulation 1966;33:778-780.
2. Tubiana R, Thomine J-M, Mackin, E. Examination of the Hand and Wrist. New York: Informa Healthcare, 2009.
3. Brzezinski M, Luisetti T, London MJ. Radial artery cannulation: A comprehensive review of recent anatomic and physiologic investigations. Anesth Analg 2009;109:1763–81.
4. Freestone B, Nolan J. Transradial cardiac procedures: the state of the art. Heart 2010;96:883-891.
5. Ronald A, Patel A, Dunning J. Is the Allen’s test adequate to safely confirm that a radial artery may be harvested for coronary arterial bypass grafting? Interactive Cardiovasc Thorac Surg 2005;4:332–340.
6. Asif M. Sarkar PK. Three-digit Allen’s test. Ann Thorac Surg 2007;84:686–847.
7. Jarvis MA, et al. Reliability of Allen’s Test in selection of patients for radial artery harvest. Ann Thorac Surg 2000;70:1362–5.
8. Ruengsakulrach P, et al. Preoperative assessment of hand circulation by means of doppler ultrasonography and the modified Allen test. J Thorac Cardiovasc Surg 2001;121:526-31.
9. Kohonen M. et al. Is the Allen test reliable enough? Eur J Cardiothorac Surg 2007;32:902-5
10. 10.  American Academy of Orthopaedic Surgeons. Clinical Practice Guideline on The Diagnosis of Carpal Tunnel Syndrome May, 2007, available at http://www.aaos.org/Research/guidelines/CTSTreatmentGuideline.pdf.
11. 11.  Vu-Rose T, et al. The Allen test. A study of inter-observer reliability. Bull Hosp J Dis 1997;56:99-101.