What is Allen's test?

What is Allen's Test

Allen's test is a bedside maneuver to assess collateral circulation to the hand by evaluating the patency of the radial and ulnar arteries, though current evidence indicates it should not be used to exclude patients from radial artery procedures.

Test Procedure

The modified Allen's test involves the following steps 1, 2:

• The examiner occludes both the patient's ulnar and radial arteries while the patient makes a tight fist, causing the hand to blanch 2
• The patient then opens the hand (without hyperextending the fingers, as this can cause false results) 2
• The examiner releases pressure on one artery (typically the ulnar) while maintaining compression on the other (radial) 2
• Normal color return to the hand within 5-6 seconds indicates adequate collateral circulation through the released artery 3
• The test is then repeated, releasing the opposite artery 2

Clinical Context and Purpose

Allen's test is performed when knowledge of hand perfusion is needed, particularly before procedures involving radial artery access 1. The test was originally described by Edgar V. Allen in 1929 for patients with thromboangiitis obliterans and was later modified in the 1950s for pre-cannulation assessment 2.

Current Evidence on Clinical Utility

The test is now considered "only of historical interest" and should not be used to deny patients radial artery access 4:

• The RADAR trial found no evidence of hand ischemia in patients undergoing transradial access, even in those with abnormal Allen's test results 1, 4
• Studies show no differences in thumb capillary lactate, grip strength, or incidence of ischemia between patients with normal versus abnormal Allen's test results who underwent transradial access 4
• An associated editorial to the RADAR trial stated that patients should not be denied transradial access based on abnormal Allen's test 1
• Reports of hand ischemia following transradial access are remarkably rare despite dramatic increases in procedures performed worldwide, and none of the reported cases demonstrated inadequate collateral circulation on pre-procedure testing 1

Test Performance Limitations

The Allen's test has significant diagnostic limitations 3:

• At the conventional 6-second cut-off, sensitivity is only 54.5% with specificity of 91.7% 3
• Even at optimal cut-off points, diagnostic accuracy reaches only 79.6% 3
• The test is susceptible to examiner error and subjective interpretation 2
• Hyperextension of fingers during the test can decrease perfusion to the palmar arch, causing false-positive results 2

Why the Test Is No Longer Recommended

The robust collateral circulation in the hand from the ulnar artery makes ischemic complications from radial artery access extraordinarily rare 4. Radial artery occlusion occurs in less than 5% of patients with current prevention strategies and is almost always clinically silent due to collateral circulation from the palmar arch 1, 4.

Common Pitfalls

• Do not exclude patients from radial artery procedures based solely on an abnormal Allen's test 1, 4
• Avoid having patients hyperextend their fingers during the test, as this causes false results 2
• Recognize that the test has poor sensitivity and should not be relied upon as the sole determinant of vascular adequacy 3