Allen's test

An altered test, first suggested by Irving S Wright in 1952, has almost universally replaced the original method in contemporary medical practice. The alternative method is often referred to as the modified Allen's test or modified Allen test.

Method

Original test

The original test proposed by Allen is performed as follows:

1. The patient is asked to clench both fists tightly for 1 minute at the same time.
2. Pressure is applied over the radial and ulnar arteries simultaneously so as to occlude them.
3. The patient then opens the fingers of both hands rapidly, and the examiner compares the colour of both. The initial pallor should be replaced quickly by rubor.
4. The test may be repeated, this time occluding the ulnar arteries.

Modified test

In the modified Allen test, one hand is examined at a time:

1. The patient is asked to clench their fist for about 30 seconds.
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 may be observed at the finger nails).
4. Ulnar pressure is released while radial pressure is maintained, and the colour should return within 5 to 15 seconds.

If color returns as described, Allen's test is considered to be normal. If color fails to return, the test is considered abnormal and it suggests that the ulnar artery supply to the hand is not sufficient.