RADAR: Abnormal Allen’s Test Should Not Prohibit Radial Access

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Results of the modified Allen’s test have no bearing on whether patients can or cannot safely undergo transradial interventions, according to a paper published online February 26, 2014, ahead of print in the Journal of the American College of Cardiology.

For the RADAR study, a team led by Marco Valgimigli, MD, PhD, of Erasmus Medical Center (Rotterdam, the Netherlands), looked at 203 patients who had elective or urgent angiography via the transradial approach from October 2007 to June 2009. All underwent the modified Allen’s test, which measures the time to achieve maximal palmar blush after compression release of the ulnar artery with continuing occlusive pressure of the radial artery.

Lactate Levels Suggest No Effect on Post-Procedural Ischemia

Allen’s test results were classified as:

  • Normal (blush within 5 seconds) in 83 patients (40.9%)
  • Intermediate (blush in 6-10 seconds) in 60 patients (29.6%)
  • Abnormal (blush after 10 seconds) in 60 patients (29.6%)

Post-procedural thumb capillary lactate, the study’s primary endpoint, did not differ across the normal (185 ± 0.93 mmol/L), intermediate (185 ± 0.66 mmol/L), and abnormal Allen’s test groups (197 ± 0.71 mmol/L; P = 0.59).

No ischemic vascular or bleeding complications occurred at the access site during or after the transradial procedure, and no patients required vascular surgery.

However, plethysmography readings showed different patterns depending on Allen’s test results (P < 0.0001). Pattern A (no damping of pulse tracing) was observed in 83% of the normal group and 2% of the abnormal group, whereas pattern D (loss of pulse tracing without recovery within 2 minutes) was seen solely in the abnormal group, at a rate of approximately 40%.

Ulnar frame count was lower both before and after catheterization in patients with normal compared with intermediate or abnormal Allen’s test results, suggesting greater ulnar blood flow. Although the difference persisted, patients with abnormal Allen’s test results at baseline showed post-procedural improvement.

Baseline characteristics were generally similar among the Allen’s test groups, although patients with abnormal results were more likely to have insulin-dependent diabetes and less likely to have previously undergone radial access than those with intermediate or normal results. In each group, patients showed similar handgrip strength and reported similar levels of discomfort.

Time for a ‘Paradigm Shift’

“Our study provides proof of concept for a paradigm shift in cardiovascular intervention as the widespread, yet unproven, belief that normal [Allen’s test] is a prerequisite for selecting patients before [transradial access] could not be confirmed,” the researchers conclude, pointing out that no clinical or subclinical signs of hand ischemia were detected in patients with abnormal results. “A confirmatory study focusing on clinical endpoints and involving a larger patient population is ongoing,” they report, citing a prespecified substudy of the MATRIX trial.

In an accompanying editorial, Olivier F. Bertrand, MD, PhD, of Laval University (Quebec, Canada), and colleagues assert that patient selection for transradial access remains a “hot topic,” with controversy over the Allen’s test at the forefront.

The main debate, they say, is whether the Allen’s test or the “more objective” plethysmography, “can reliably predict a significant ischemic risk for the hand, presumably due to periprocedural [radial artery occlusion].” Moreover, it remains to be seen if acute radial artery occlusion has much clinical relevance, they point out.

“Based on the RADAR results, we believe that the denial of radial access for diagnostic angiography or interventions based solely on an abnormal [Allen’s test] or oximetry-plethysmography curve is not warranted since these tests are not scientifically predictive of pathologic rises in lactate levels, weakness in the hand, or persisting discomfort during or after transradial catheterization,” the editorial authors conclude. “Time has come to remove the Allen’s test from preprocedural triage for transradial catheterization.”

Palpable Radial Artery Is Enough

In an e-mail, Dr. Valgimigli said that a shift in practice has already occurred. Many operators have stopped using the test, and based on the current study, he added, it is “difficult to justify its performance.”

The radial approach should be pursued “every time it is feasible, irrespective of the Allen’s test results,” he argued.

R. Lee Jobe, MD, of Wake Heart and Vascular (Raleigh, NC), agreed that it is time for the Allen’s test to go. He told TCTMD in a telephone interview that, at this point, US radialists are more likely than their European or Japanese counterparts to evaluate perfusion to the hand.

“I think it’s primarily because we’re cautious in the United States. We’re in a different medico-legal environment,” he said, adding that “most operators in the United States don’t have that much experience with radial. They haven’t done thousands of these procedures, . . . and [the Allen’s test] just adds a small layer of confidence.”

However, “perfusion to the hand is more complex than just 2 arteries (1 radial and 1 ulnar), especially now that we’re using smaller and smaller catheters,” Dr. Jobe noted, reporting that 5-Fr is now the norm. “As catheters get smaller, this really becomes a [nonissue]. The tradition for most operators in Europe at high-volume experienced centers has always been, ‘If you can feel the radial pulse, just do it,’” he commented.

Importantly, ischemic outcomes are predicted less by Allen’s test results than “by how we manage the radial artery after the catheter comes out,” Dr. Jobe explained, citing the concept of patent hemostasis, where operators remove the support band from the radial artery as quickly as possible in order to minimize the risk of long-term radial artery occlusion.

Study Details

A total of 942 patients were screened. The researchers enrolled subjects consecutively until the prespecified number of at least 60 patients was reached in each Allen’s test group with even distribution in the normal, intermediate, and abnormal groups.


1. Valgimigli M, Campo G, Penzo C, et al. Trans-radial coronary catheterization and intervention across the whole spectrum of Allen’s test results. J Am Coll Cardiol. 2014;Epub ahead of print.

2. Bertrand OF, Carey PC, Gilchrist I. Allen or no Allen: that is the question! [editorial]. J Am Coll Cardiol. 2014;Epub ahead of print.



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  • Dr. Valgimigli reports financial relationships with several drug and device companies.
  • Drs. Bertrand, Carey, Gilchrist, and Jobe report no relevant conflicts of interest.