The Allen Test for Blood Flow

Original Editors - Alexander Ghyssels

Top Contributors - Sue Safadi, Alexander Ghyssels, Sheik Abdul Khadir, Claire Knott, Admin, Rachael Lowe, Scott Cornish, Kim Jackson, Tarina van der Stockt, Magdalena Hytros, George Prudden, Kai A. Sigel, WikiSysop and Shaimaa Eldib  

Introduction 

• The Allen test is a worldwide used test to determine whether the patency of the radial or ulnar artery is normal. It is performed prior to radial cannulation or catheterisation, because placement of such a catheter often results in thrombosis. Therefore the test is used to reduce the risk of ischemia to the hand. The Allen test can also be used to gather information preceding removal of the radial artery for a coronary bypass graft.
  
•  A positive Allen’s test means that the patient does not have dual blood supply to the hand, which is a negative indication for catheterisation or removal of the radial arteries.
• There is also a digital Allen’s test, which is used to assess the arterial supply to the fingers.
• In the physiotherapy  it is often used as a diagnostic procedure for the thoracic outlet syndrome.
  
  

Clinically Relevant Anatomy

• The supply in the arm starts in the neck between the scalenus muscles. It is the subclavian artery who supply the arm from above. The subclavian artery becomes the arteria axillaris, who becomes after 3 inches an arteria brachialis. In the region af the elbow (fossa cubita) divides the arteria in two pieces: the ulnar artery and the radial artery.
  
•  The hand has a complex and rich vascular network, which in most cases is provided by the radial and ulnar artery.
• The radial artery runs between the musculus brachioradialis and musculus flexor carpi radialis. At the wrist, it splits into a superficial branch to contribute to the superficial palmar arch. The other branch crosses dorsally deep to the tendons of the anatomic snuffbox to form the deep palmar arch.
• The ulnar artery lies under the musculus flexor carpi ulnaris. At the wrist it enters the Guyons canal, where it splits into a deep palmar branch and a superficial palmar branch. The superficial palmar branch forms the superficial palmar arch, while the deep branch contributes to the deep palmar arch.
• Since the radial as well as the ulnar arteries both form anastomosis (cfr. the deep and superficial palmar arch) the blood supply of the hand is ensured even if one of the arteries is occluded, In that case the other one can take charge of the blood supply.
• There are also neurological structures that are involved in TOS. The plexus brachialis of who passes in the neck between the scalenus medius and scalenus anterior are compressed by the hypertonity of the neckmuscles. That is what we called neuropraxis.
  

Epidemiology 

In 3% of the hospitalised patients an inadequate collateral blood supply was diagnosed by Allen’s test. 

Differential Diagnosis

The allen’s test can be an instrument for different disorders.
The test can be used for all the diseases with insufficient vascularisation in the arm. A thoracic outlet syndrome is an example for that.
A compartiment syndrome can also be investigated by an allen test.
But it is most frequently used after a bypass operation of the hand. With a good interpretation of the test, the surgeon can see if the blood supply is normal in the hand.

• Two arteries normally supply blood to the hand. The blood flow in both arteries is stopped until your hand becomes pale.
  
•  Blood is then allowed to flow through the artery that will not be used to collect the blood sample.
• If this artery is working well, your hand will quickly regain its normal color. This means that an accidental injury to the artery used for collecting the blood sample will not completely block all blood flow to your hand.
• If the artery that will not be used to collect the blood sample is not working well, your hand will remain pale. The Allen test will then be performed on your other hand. If it also remains pale, the blood often will be collected from another artery, usually in the groin or elbow crease.
  
  

Diagnostic Procedures

The allen’s test is frequently used for looking if the radial artery is usefull for a coronary bypass grafting.
We don’t use it as a physiotherapist in practice to determine that kind of issues.
The therapist has to interpret the results carefully.
If the hand becomes bleach at the 3 first digits, there is a lack in the radial artery.

Outcome Measures

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Examination

The examiner flexes the patient's elbow to 90 degrees while the shoulder is extended horizontally and rotated laterally. The patient is asked to turn their head away from the tested arm. The radial pulse is palpated and if it disappears as the patient's head is rotated the test is considered positive.
There is also a modified allen’s test. The examiner blocks first the ulnar artery and asks the patiënt to flex and extend the vingers rapidly. The therapist compare with the other hand. After the ulnar artery, we do the same with the radial artery.

Medical Management

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Physical Therapy Management

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Key Research

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Resources

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Clinical Bottom Line

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