ALLEN TEST ; An Assessment of Collateral Circulation

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The Allen test comes under a diagnostic test which is performed at the patient’s bedside. This test is done, mainly to know the patency of your hand’s arteries and also can help the health professional to be sure that the both arteries( radial and ulnar) are doing their job ( i.e. supply oxygenated blood to the hands) properly. It is also called the modified Allen test.

 

History

 

Edgar Van Nuys Allen ,an American doctor described the original version of this test called Allen, in 1929. According to Edgar V. Allen , it is an non-invasive procedure, mostly used to assess the arterial blood flow to the hand.  For the first time , he did this physical examination on a patient with thromboangiitis obliterans ,simply to know his hand’s arterial patency.

 

Common sites

There are two common sites for this test. Like;

  1. Radial artery

  2. Ulnar artery

 

Alternative sites

 There are also three alternative sites . like;

  1. Brachial artery at the antecubital fossa

  2. Femoral artery which is situated just below the inguinal ligament

  3. Dorsalis pedis ,present at the foot.

 

Need of an allen test

 

  • This test is always recommended by the physician before cannulating the radial artery.

  • Before the wrist surgery or any other surgeries related to your hands.

  • Somehow the radial artery is chosen as a conduit for heart bypass surgery rather than saphenous vein because of its patency.

  • Before the dialysis of kidney

  • To know the lung ventilation(Pco2) , tissue oxygenation(po2) and acid-base status( ph,pco2, pHco3) ,we have to do an arterial blood gas test. But, before that Allen test was performed.

 

Technique

 

following are some simple techniques which are the health professionals used during the test ;

  1. Instruct the client to take position ( mainly fowler’s position) with a pillow just under the hands.

  2. Tell him to be relaxed and keep the hand with the palm facing upward.

  3. Locate the radial and ulnar artery of the hand by using index and middle fingers( this process is called palpation).

 

Position of the arteries

  • The radial artery is present just below the thumb at the proximal region of the wrist . Besides it the radial artery is very easily palpable.

  • The ulnar artery is very narrow and it’s very difficult to find out. But usually it is found on the side of the little finger.

 

  • After palpation, put pressure on the radial and ulnar artery at a time with the three fingers or the thumb.

  • Check the palm and fingers, whether it became pallor( blenched) or not.

  • Then slowly release the ulnar artery .

  • Note the time taken , the hand by changing its color from pallor to erythematous. Basically, it indicates the collateral blood flow returns.

  • The same procedure should be done on the radial artery by holding the ulnar . 

  • Note the time in the same way .

  • Then compare the both and evaluate whether the collateral blood flow is normal or not.

 

Results

  • Positive Allen test – if the color of the hand and fingers change from pallor to erythematous in 5-15 seconds , then the test is considered to be positive(+). Which means you have a normal collateral blood flow to your hands.

 

  • Negative Allen test – if the color of the hand and fingers don’t change from pallor to erythematous in 5-15 seconds , then the test is considered to be negative(-).which means you have an abnormal collateral blood flow to your hands.  

 

Contra-indications

  • The patient with poor collateral blood flow on the hands .

  • The widely separated fingers with hyperextended hands give a false positive result.

  •  This test should not be applied on the patient who is uncooperative or in sedation. So, for them the alternative methods should be used like; pulse plethy sonography and doppler flow measurement etc. but these are not validated .

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