What is the procedure for performing Allen's test?

How to Perform Allen's Test

Allen's test is no longer recommended as a routine procedure for assessing collateral circulation of the hand prior to radial artery access, as it has been shown to be an unreliable predictor of hand ischemia and should not preclude transradial access. 1

Traditional Allen's Test Procedure

Despite its limitations, understanding the traditional Allen's test procedure remains relevant for historical context:

• Have the patient elevate their hand and make a tight fist for 30 seconds to exsanguinate the hand 2
• Compress both the radial and ulnar arteries at the wrist simultaneously 2
• Ask the patient to open their hand (without hyperextending the fingers) 2
• The hand should appear blanched (pale) due to arterial occlusion 2
• Release pressure on the ulnar artery while maintaining compression of the radial artery 2
• Observe for return of normal color to the hand, which traditionally indicated adequate collateral circulation through the ulnar artery 2

Current Guidelines and Evidence

• According to the American Heart Association (2018), performing Allen's or Barbeau test to confirm dual arterial circulation to the hand is "only of historical interest" 1
• Recent studies have found no differences in thumb capillary lactate, grip strength, or incidence of ischemia between patients with normal and abnormal Allen's test results who underwent transradial access 1
• The RADAR trial found no evidence of hand ischemia in patients undergoing transradial access, even in those with abnormal Allen's test results 1
• Cardiac specialists no longer confirm collateral circulation to the hand with Allen's test as it does not predict hand ischemia 1

Limitations of Allen's Test

• At a conventional cut-off of 6 seconds, Allen's test has a sensitivity of only 54.5%, specificity of 91.7%, and diagnostic accuracy of 78.5% 3
• Even at its optimal cut-off point of 5 seconds, diagnostic accuracy is only 79.6% 3
• The test is susceptible to error and subjective interpretation 2
• Reports of hand ischemia following transradial access are remarkably rare despite the dramatic increase in transradial procedures worldwide 1

Alternative Assessment Methods

• Ultrasound imaging may be helpful in identifying an occluded radial artery that fills via retrograde collaterals 1
• The reverse Allen or Barbeau test may also help identify occluded radial arteries 1
• Doppler ultrasound testing of the ulnar collateral circulation is more objective and reliable 3, 4
• Quantitative measurement of digital systolic pressure during compression of the radial or ulnar artery provides more accurate assessment 5

Current Best Practice

• Routine application of the Allen or Barbeau test is not a useful triage strategy for radial artery access 1
• An abnormal Allen's test should not preclude transradial access 1
• Patients should not be denied a radial approach simply because of a "failed" Allen test 1
• Assessment of the radial pulse remains important, but the Allen's test is no longer considered necessary 1

Clinical Considerations

• The robust collateral circulation in the hand from the ulnar artery makes ischemic complications from radial artery access extraordinarily rare 1
• Radial artery occlusion occurs in less than 5% of patients with current prevention strategies and is almost always clinically silent due to collateral circulation 1
• Ultrasound guidance increases the speed and efficacy of transradial access, decreasing time to access and number of attempts 1