Allen’s Test

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Definition

Allen’s test is a used to test the blood supply in the hand that is performed before radial arterial blood sampling or cannulation. It is also called as Allen test.

image credit: texasheart.org

image credit: texasheart.org

Etymology

The test is named after Edgar Van Nuys Allen.

Purpose
  1. This test is used to determine adequate collateral blood flow in the hand by evaluating the patency of the radial and ulnar arteries.
  2. Allen test determines whether ulnar circulation is inadequate or nonexistence. Once inadequate or nonexistence of ulnar circulation is noted the radial artery supplying arterial blood to that hand should not be punctured once.
Procedure
  1. Check the patient’s identity and explain the procedure to ensure that correct client undergoes the procedure and promote coordination of the client.
  2. Instruct the patient clench his/her fist, or if the patient is unable, you may close the hand tightly. This removes as much blood from the hand as possible.
  3. Using your fingers, apply direct pressure to the radial and ulnar arteries to obstruct the arterial blood flow to the hand.
  4. Have the client open his or her hand while applying occlusive pressure to both arteries. Fingers and hand should be pale and blanched which indicates lack of arterial blood flow.
  5. Release the pressure over the ulnar artery. Observe color of fingers, thumbs and the hand. Fingers and hand should flush within 15 seconds.
  6. Repeat procedures 2 to 5 with the other hand.

Interpretation of Results

Flushing is a positive Allen’s test. If test is negative, no flushing, radial artery should be avoided. If collateral circulation to hand is present through ulnar arteries, the hand and the fingers should flush. Ulnar artery can supply blood flow if radial artery is damaged or becomes occluded during the procedure. When the hands and fingers flush within 15 seconds, a positive Allen’s test, arterial puncture can be done.