Allen's test

Allen's Test

examination of arterial blood flow to the handright

Allen's Test, also known as the Allen Test, is a vital medical sign used in the physical examination of arterial blood flow to the hands. This test plays a crucial role in assessing the integrity of the arterial supply to the hand and is named in honor of Dr. Edgar Van Nuys Allen, who originally described the test in 1929. Over time, modifications and improvements to the test have been made, and a widely accepted alternative method, known as the Modified Allen's Test or Modified Allen Test, has become the standard in contemporary medical practice.

Purpose

The primary purpose of Allen's Test is to evaluate the patency and adequacy of blood flow through the radial and ulnar arteries in the hand. This assessment is particularly important before performing procedures that may compromise arterial circulation, such as arterial line placement, cardiac catheterization, or hand surgeries. By assessing both the radial and ulnar arteries, healthcare professionals can determine if one of these arteries is compromised, allowing them to choose the optimal site for arterial access.

Procedure

The traditional Allen's Test involves the following steps:

• 1. The patient is seated comfortably, and their hands are elevated to ensure venous drainage.
• 2. The examiner compresses both the radial and ulnar arteries in the patient's wrist, effectively blocking blood flow to the hand.
• 3. The patient is then asked to make a fist several times to remove any remaining oxygenated blood from the hand.
• 4. The examiner releases pressure on one of the arteries (typically the ulnar artery), while continuing to block the other (radial artery).
• 5. The patient is instructed to open their hand fully, which should now appear blanched or pale.
• 6. The examiner observes the speed at which normal color and perfusion return to the hand. If this occurs within approximately 5-15 seconds, it is considered a positive Allen's Test, indicating adequate collateral circulation.

Modified Allen's Test

The Modified Allen's Test is an updated version of the original test, offering greater reliability and precision. In this method, the examiner only compresses the radial artery while leaving the ulnar artery open. The rest of the procedure remains the same. This modification has almost universally replaced the original method in modern medical practice due to its improved accuracy and patient comfort.

Clinical Significance

A positive Allen's Test, whether using the traditional or modified method, suggests that there is adequate collateral circulation in the hand. This means that occluding one of the major arteries (radial or ulnar) will not significantly compromise blood supply to the hand. In contrast, a negative Allen's Test indicates insufficient collateral circulation, making the occluded artery an unsuitable site for medical procedures.

See Also

• Arterial Blood Gas
• Pulse Oximetry
• Vascular Surgery