It has long been Dogma that an abnormal modified Allen’s test is a contraindication to performing a radial arterial line in that arm. The theory behind this is that the modified Allen’s test will identify patients who have insufficient collateral circulation via the ulnar artery and the deep and superficial palmar arch placing the digits at risk for ischemic injury. This has long been a controversial area but now mounting evidence supports that radial arterial cannulation is safe even in patients who have an abnormal modified Allen’s test.
During a modified Allen’s test, the patient makes a tight fist and elevates the wrist for 30 seconds. Then, the operator compresses both the ulnar and radial artery and the hand is opened and should appear blanched. Finally, the hand is lowered and pressure on the ulnar artery is released. Reperfusion of the hand should occur within 7 seconds normally. If it takes longer than 7 seconds for a pink color to return to the hand, it is considered an abnormal modified Allen’s test.
The reliability of the modified Allen’s test to predict ischemic complications for radial artery cannulation has been questioned by numerous studies. Jarvis and colleagues in 2000 determined that the Allen’s test had poor predictive value for assessing which patients could undergo radial artery harvesting.[1] In 1983, Slogoff and colleagues studied nearly 1,800 patients who underwent radial artery cannulation and nearly 25% of them had radial artery occlusion with no adverse ischemic consequences.[2] A review of the literature in 1985 also supports the notion that the modified Allen’s test is a poor predictor of ischemic complications from radial arterial line placement.[3]
Now, a new prospective randomized controlled trial has investigated whether the Allen’s test can predict adverse outcomes in patients undergoing transradial coronary catheterization (RADAR trial).[4] This trial investigated over 200 patients and found that there were no adverse events, including ischemic complications, in patients with abnormal Allen’s test compared with those with a normal Allen’s test.
This is further support that a pre-procedure modified Allen’s test is not a reliable predictor of ischemic complications for radial arterial line insertion and an abnormal Allen’s test should not be a contraindication to placing a radial arterial line.
FAQS
Allen test vs modified Allen test. Which one do you prefer? How do they differ?
The modified Allen test differs from the original by evaluating the radial and/or ulnar arteries on one hand, then repeating on the other side if necessary. Unlike the traditional approach, where the patient’s arm is flexed and the fist clenched to exsanguinate the hand, this modified version allows for a more systematic assessment of vascular competency and perfusion.
What is the modified Allen test used for?
The purpose of a modified Allen test is to assess arterial competency, and it is recommended to be conducted before obtaining an arterial sample.
When performing the Allen test, which artery is released first?
[1] Jarvis MA, Jarvis CL, Jones PR, Spyt TJ (October 2000). “Reliability of Allen’s test in selection of patients for radial artery harvest”. Ann. Thorac. Surg. 70 (4): 1362–5 [2] Slogoff, S; Keats AS; Arlund C (1983). “On the safety of radial artery cannulation.”. Anesthesiology 59: 42–7 [3] Wilkins, RG (1985). “Radial artery cannulation and ischaemic damage: A review.”. Anaesthesia 40: 896–899 [4] Marco Valgimigli, MD, PhD et al. Transradial Coronary Catheterization and Intervention Across the Whole Spectrum of Allen Test Results. J Am Coll Cardiol. 2014;63(18):1833-1841