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How to Perform a Modified Allen Test (What is the Purpose of the Test?)

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Are you ready to learn how to perform a Modified Allen Test? Or maybe you’re wondering what is the purpose of the Allen’s Test? If so, you’re in the right place because that is what this article is all about.

 Modified Allen Test

So if you’re ready, let’s go ahead and dive right in.

What is the Modified Allen Test?

The Allen Test for assessment of blood flow was originally developed by Edgar V. Allen in 1929 as a non-invasive method of assessing the patency of a patient’s arteries. Since then, it has been adopted as the Modified Allen Test, and is used to check for collateral circulation of the radial and ulnar arteries in the wrist.

The difference between the Modified Allen Test and the original Allen Test is that Modified Allen Test efficiently evaluates the adequacy of blood circulation on one hand at a time.

The Modified Allen Test measures the competency and quality of the artery and should be performed prior to performing an arterial puncture.

How to Perform a Modified Allen Test (Step by Step):


Step 1: Have the Patient Make a Fist

Instruct the patient to clench his or her fist in order to enhance the circulation within the arteries. If the patient lacks the ability to do so, you can assist by manually closing the fist for them.

Step 2: Locate the Radial and Ulnar Arteries

Face the patient and locate the radial and ulnar arteries. The radial artery is located on the thumb side of the wrist on the underside of the forearm, while the ulnar artery is on the pinky side of the wrist.

Make sure to locate both the radial and ulnar pulses.

Step 3: Grab the Patient’s Hand

Using your right hand, slowly grab the patient’s left hand. You can also use your left hand to grab the patient’s right hand if that is your preference.

Do whichever is more comfortable to both you and the patient.

Step 4: Locate the Pulse

Place your middle finger on top of the radial pulse and your pointer finger on the ulnar pulse of the patient.

Step 5: Apply Pressure to Both Arteries

When both pulses can be felt, apply occlusive pressure to both the ulnar and radial arteries to temporarily stop the blood circulation of the hand.

Be sure to tell the patient to relax his or her hand while doing this.

Step 6: Have the Patient Open Their Hand

This is done to check whether the palm and fingers have blanched.

Blanching means that you have completely occluded the radial and ulnar arteries with your fingers. At this time, the hand should have a white-ish appearance in color.

Step 7: Slowly Release the Pressure on the Ulnar Artery

You can release pressure on the ulnar artery while keeping the radial artery occluded. The patient’s hand should flush within 5 to 15 seconds, meaning that it should turn pink. If it does, this indicates that the ulnar artery is patent and has good blood flow.

This is considered a positive Modified Allen Test and you can proceed to stick and collect the ABG sample at this site.

However, if flushing is not observed within 5 to 15 seconds, this result suggests that collateral circulation is not present and this is considered as a negative Modified Allen Test.

In this case, it is recommended not to puncture the radial artery at this site. You should either try the Modified Allen Test on the other hand or move on to the brachial artery.

Final Thoughts

So there you have it. That pretty much wraps up everything you need to know about performing a Modified Allen Test.

Be sure to perform the Modified Allen Test before each and every ABG stick that you perform on a patient. It’s important to do so because the test helps to check for collateral circulation in the radial and ulnar arteries.

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