Allen Test: How to Check for Arterial Blood Flow in the Hand

The Allen Test is a vascular assessment used to check the patency of the radial and ulnar arteries in the hand. It is a critical test performed before procedures like an arterial blood gas (ABG) draw or arterial line placement.

1. Purpose

The primary purpose is to **test for** the patency (openness) of the Radial and Ulnar arteries in the hand. It checks for sufficient collateral (backup) blood flow. This is commonly performed before an arterial blood gas (ABG) draw or arterial line insertion to ensure the hand will still get blood if one artery is blocked.

2. How to Perform

1. The patient is positioned in sitting.
2. The patient is asked to open and close their hand (make a fist) several times to pump blood out of the hand.
3. The patient is then asked to make a tight fist.
4. The examiner uses their thumbs to apply firm pressure over both the Radial and Ulnar arteries at the wrist, occluding them.
5. While maintaining pressure, the examiner instructs the patient to open their hand. The palm should appear blanched (pale).
6. The examiner releases pressure on the Ulnar Artery (while keeping pressure on the radial).
7. The examiner observes how long it takes for color to return (this tests the ulnara artery).
8. The test is repeated, but in step 6, the examiner releases pressure on the Radial Artery (this tests the radial artery).

3. Positive & Negative Sign

Note: The terms 'positive' and 'negative' can be confusing. It is clearer to use 'normal' and 'abnormal.'

Normal Finding (Test is NEGATIVE for occlusion):
This indicates a good result.

• Color returns to the entire palm within 5-10 seconds. This indicates the released artery is patent and collateral circulation is good.

Abnormal Finding (Test is POSITIVE for occlusion): This indicates a poor result.

• Color return is delayed (>10-15 seconds) or does not return to parts of the hand. This indicates occlusion or poor patency in the released artery.