Allen test

The modified Allen test (MAT) may be used to clinically assess the patency and completeness of the superficial palmar arch . Its classic use is in assessing for sufficient collateral flow to the hand, to avoid ischemia in the setting of radial artery puncture, cannulation, catheterization or radial artery harvest for coronary revascularization .

Procedure

In the MAT, the patient is required to clench their fist for thirty seconds, while external pressure is applied to occlude both the radial and ulnar arteries. The patient then opens their fist and the ulnar artery is released (with the radial artery still occluded). The result is considered positive (abnormal) if the hand fails to return to its normal color after an extended period. This period is subject to considerable debate, and can range between 3 and 12 seconds.

Evidence

The evidence to support the accuracy of the MAT is weak; both the original Allen test (which was superseded by the MAT) and the MAT itself exhibit low sensitivity for evaluation of collateral circulation . One systematic review concluded that the MAT lacks sufficient diagnostic validity to support its use in screening collateral circulation deficits of the hand. It was also found to be a poor and unreliable predictor of hand ischemia post-arterial puncture.

In most patients, the MAT is rarely performed; ultrasound is generally preferred for achieving the same purpose with greater sensitivity in patients requiring coronary revascularization .

History and etymology

The original Allen test was first described in 1929 by Edgar V. Allen, as part of a report on three patients with thromboangiitis obliterans. Later that same year, Irving S. Wright proposed the modified Allen test, which quickly and completely replaced the original method .