Allen Test

Contents

Introduction [1][2][3][4]

  • 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.

Clinically Relevant Anatomy[5][6]

  • 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.

Epidemiology 

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

Differential Diagnosis[7]

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[8]

The allen’s test is frequently used for looking if the radial artery is usefull for a coronary bypass grafting.
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.

Examination [9]

The patient is asked to open and close the hand several times as quickly as possible and then squeeze the hand tightly . The examiner's thumb and index finger are placed over the radial and ulnar arteries, compressing them . As an alternative technique, the examiner may use both hands ,placing one thumb over each artery to compress the artery and placing the fingers on the posterior aspect of the arm for stability. The patient then opens the hand while pressure is maintained over the arteries. One artery is tested by releasing the pressure over that artery to see if the hand flushes. The other artery is then tested in a similiar fashion. Both hands should be tested for comaprison . 


[10]

Specificity & Sensitivity [11]

Martin et al (2000) reported a sensitivity of 73.2% and a specificity 97.1%. Based on these findings we can establish that the Allen test is a good and valid screening test for the circulation of the hand.

 

Recent Related Research (from Pubmed)

References

  1. J.G. Seiler et al. Essentials of hand surgery, American society for surgery of the hand, lippincot Williams and Wilkins, 2002
  2. Andrew Ronald et al. Is the Allen's test adequate to safely confirm that a radial artery may be harvested. CardioVasc Thorac Surg 2005;4:332-340
  3. Christine B. Novak. Outcome Following Conservative Management of Thoracic Outlet Syndrome. J Hand Surg 1995;20A:542-548.)
  4. Adam J. Hansen. Reverse Radial Forearm Fascial Flap With Radial Artery Preservation. American Association for Hand Surgery 2007
  5. Joints and associated structures of the hand, University of Michigan medical school, 1995
  6. S. Moses, Cardiovascular medicine book, family practise notebook, 20/02/2011
  7. Adam J. Hansen. Reverse Radial Forearm Fascial Flap With Radial Artery Preservation. American Association for Hand Surgery 2007
  8. Marek Brzezinski et al. Radial Artery Cannulation: A Comprehensive Review of Recent Anatomic and Physiologic Investigations. Anesth Analg 2009;109:1763–81)
  9. David J Magee : Orthopedic Physical Assessment:fifth edition; In:Forearm,Wrist and Hand;Chapter seven;pg-445-446.
  10. Physiotutors. Allen Test⎟Hand Vascularisation. Available from: https://www.youtube.com/watch?v=D1tJO0RW9UM
  11. A. Martin et al. Reliability of Allen’s test in selection of patients for radial artery harvest, The society of thoracic surgeons. Ann Thorac Surg 2000;70:1362-1365