Radial catheterization allen's test

Pre-procedure assessment
The hand is normally supplied by blood from the ulnar and radial arteries. The arteries undergo anastomosis in the hand. Thus, if the blood supply from one of the arteries is cut off, the other artery can supply adequate blood to the hand. A minority of people lack this dual blood supply. Allen's test or oximetry/plethysmography should be performed before the procedure to confirm that there is sufficient blood flow in the ulnar artery should there be a loss of patency in the radial artery due to either thrombosis or spasm which can result in gangrenous finger or had loss.

Performance of the Allen's Test Before the Radial artery catheterization
This test is named after Edgar Van Nuys Allen. .The utility of the Allen's test has been questioned, and no direct association with ischemic complications of radial artery cannulation have ever been demonstrated. In 1983, Slogoff and colleagues reviewed 1,782 radial artery cannulations and found that 25% of them resulted in complete radial artery occlusion, without apparent adverse effects. A number of reports have been published in which permanent ischemic sequelae occurred even in the presence of a normal Allen's test. In addition, the results of Allen's tests do not appear to correlate with distal blood flow as demonstrated by fluorescein dye injections or photoplethysmography.

Modifications to the test have been proposed to improve reliability.

Despite this lack of association with outcomes, the Allen's Test is often performed in clinical practice.

How to Perform The Allen's Test
1) The hand is elevated and the patient/person is asked to make a fist for about 30 secs.

2) Pressure is applied over the ulnar and the radial arteries so as to occlude both of them.

3) Still elevated, the hand is then opened. It should appear blanched (pallor can be observed at the finger nails).

4) Ulnar pressure is released and the color should return in 7 secs.

Inference: Ulnar artery supply to the hand is sufficient and it is safe to cannulate the radial artery

If color does not return or returns after 7 seconds, then the ulnar artery supply to the hand is not sufficient and the radial artery therefore cannot be safely cannulated.

Below is a video demonstrating Allen's test



Reverse Allen's test may be performed in patients who require a second procedure through the same radial site. In reverse Allen's test, the physician releases pressure over the radial artery rather than the ulnar. This may detect proximal radial artery disease/occlusion that may be asymptomatic. Patients with an abnormal Reverse Allen's Test should not undergo a repeat transradial procedure from same radial site.