Allen test

The Allen test is a clinical test instrument that functionally examines the blood flow in the hand through the radial and ulnar arteries.

The Allen test is a simple and meaningful test instrument that can be performed, for example, before removing the radial artery to create an arterial bypass, and checks the collateral supply of the hand. The aim is to ensure sufficient arterial supply to the hand, even after any necessary removal of the vessel.

In addition to diagnostics before a bypass operation, the Allen test is also a clinical instrument for further diagnostics of Raynaud's syndrome, PAD or, for example, for testing the creation of an aterial access to the radial artery.

Procedure:

First the examiner compresses the radial artery as well as the ulnar artery. Afterwards, the patient closes his hand several times to his fist to pump out the venous blood until the palm turns white. By selectively opening the manual compression of the radial or ulnar arteries, the examiner now checks whether the collateral supply of the hand guarantees blood circulation. Normally, the collateral supply of the hand means that one of the arteries is sufficient to supply the whole hand with arterial blood.

If the hand quickly turns pink (approx. 5-7 sec.) after opening the compression, the Allen test is inconspicuous. If the rapid reperfusion does not occur or if this time is significantly longer, this is an indication of an occlusion or arteriosclerosis of the respective artery.

The therapy depends on the cause of the pathological Allen test. If the collateral supply of the hand, e.g. by a total occlusion, is not guaranteed, a removal of the artery for the bypass is out of the question. If, for example, only an extension of the reperfusion time is shown, this is an indication of sclerosis of the arteries, which can then be treated systemically if necessary.

However, the decision depends largely on the examination findings and the underlying disease.

Herold, Internal Medicine, Edition 2018, p. 821