Allen Test of the Hand. What does the most up-to-date studies says?
The Allen Test is a popular and easy technique used to assess collateral circulation in the hand previous interventions such as cateterisms. However, what does the current evidence affirms about its reliability and validity?
We bring you a systematic review from 2017 published in the journal “Emergencias” in which this procedure, which is frequently used in hospitals and healthcare centers, is called into question.
The Allen test, also known as the Allen’s maneuvre, it´s typically performed before catheterization or puncture of the radial artery in the hand. But, What does the literature says?
How the Allen Test is performed?
It involves asking the patient to close their hand into a fist. Then the therapist compresses the ulnar and radial arteries on the hand and occludes circulation. Once this maneuvre is performed, the therapist observe how the color of the palm of the hand becomes pale. At this point, the pressure on the ulnar artery is released, and the time it takes to return to a normal skin color is recorded. This protocol is then repeated with the radial artery.
The time it takes for recovering the normal color should indicate the degree of colateral blood flow. The test is positive when the perfusion is normal and color is restored normally. Persisten pallor in the palm indicates inadequate collateral blood flow to the hand.
According to the literature, it will be considered positive when it takes more than 10-15 seconds, indicating a possible ischemic condition. However, in subsequent studies, it is not clarified what the appropriate time frame should be. In this review, a time of 10 seconds was agreed upon since most texts considered this value valid. However, there is significant heterogeneity in the different studies conducted with this test.
Weaknesses of the Allen Test
The Allen test present several limitations:
❌ It requires the patient’s cooperation for proper execution and does not provide information about the vascular anatomy of the hand
❌ there is no unanimous agreement on the ideal arterial compression time
❌ the interpretation of the test results is not objective
❌ the technique’s procedure can generate false positives (due to forced wrist hyperextension during the test) or false negatives (due to insufficient compression of the radial artery).
Therefore, it is concluded that it is not a definitive test when assessing vascular supply and should be complemented with other tests such as Doppler ultrasound or pulse oximetry.
Nevertheless, vascular problems at the hand level (such as post-catheterization puncture) are rare due to the arterial palmar arch’s anatomy, which allows compensation through collateral circulation in the event of occlusion of one of the two arteries. Hence, another variable to be considered should be the state of collateral circulation in the hand.
P.D.: It is estimated that 20% of the population does not have a complete palmar arterial arch, so hand revascularization through the ulnar artery would be incomplete, as shown in this image.
ReHand in Musculoskeletal pathology of the Wrist, hand and Fingers
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References:
Romeu-Bordas Ó, Ballesteros-Peña S. Validez y fiabilidad del test modificado de Allen: una revisión sistemática y metanálisis. Emergencias 2017;29:126-135.
Sandker S, Hondebrink E; Grandjean J, Steenbererg W. Laser Speckle Contrast Analysis for Quantifying the Allen Test: A Feasibility Study. Lasers in Surgery and Medicine 46:186–192 (2014).
Pablo Rodríguez Sánchez-Laulhé
PhD Candidate | Hand Therapy and eHealth Researcher
