The Allen Test for Blood Flow

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Purpose [edit | edit source]

The Allen test for blood flow should not be confused with the following, similarly-named tests:

    • The modified Allen test
    • The Allen's test -
    • The digital Allen test - used to assess arterial blood flow to the fingers

The Allen test for blood flow, now also known as the Three-digit Allen's test was first described in 1929 by Edgar V. Allen. [1] [2]

The Allen test is a first line standard test used to assess the arterial blood supply of the hand. It is a valuable clinical test for patency of arteries and arterial arches in the hand [3]. This test is performed whenever intravascular access to the radial artery is planned or for selecting patients for radial artery harvesting, such as for coronary artery bypass grafting or for forearm flap elevation [4][3][5]. Based on the criteria of the modified Allen test a positive test indicates that the artery being tested has good blood flow[6].

The Allen test is part of the diagnostic work up for vascular abnormalities of the upper limb such as in thoracic outlet syndrome (TOS) [3]. In thoracic outlet syndrome and specifically vascular TOS, one possible cause can be the compression of the subclavian artery or vein as it passes through the interscalene triangle by the muscle bodies of the scalene where there can be muscular hypertrophy.

Clinically Relevant Anatomy[edit | edit source]

The hand has a complex and rich vascular network, which is mostly supplied by the radial and ulnar arteries.

The radial artery runs between the brachioradialis and flexor carpi radialis muscles of the forearm and at the wrist 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 [7].

The ulnar artery lies under flexor carpi ulnaris of the forearm and at the wrist 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 [8].

Since the radial and ulnar arteries both form anastomosis (the deep and superficial palmar arch) the blood supply of the hand is ensured even if one of the arteries is occluded,

[8]

Technique[edit | edit source]

The Allen Test for blood flow[edit | edit source]

During the Allen test, digital compression of both ulnar and radial arteries at the level of the proximal wrist crease is applied, which causes palmar blanching followed by release of compression on either artery, which causes hyperaemia in the non-diseased state.[3]

The radial artery is located by palpation at the proximal skin crease of the wrist and then compressed with three digits. The ulnar artery is similarly located and then compressed with three digits. With both arteries compressed, the subject is asked to clench and unclench the hand 10 times. The hand is then held open, ensuring that the wrist and fingers are not hyperextended and splayed out. The palm is observed to be blanched. The ulnar artery is released and the time taken for the palm and especially the thumb and thenar eminence to become flush is noted. If the capillary refill time is less than 6 seconds the test is considered positive. The test is then completed with the radial artery tested in a similar fashion [9]. Both hands should be tested for comparison. 

When performing the Allen’s test, hyperextension of the hand and wide separation of the fingers can lead to a false negative result [9]. This is due to occlusion of the transpalmar arch, and parts of the fingers and palm will continue to remain blanched after release of the ulnar artery [10]. To prevent this from occurring the test should be performed with the hand partially open as originally described by Allen’s [1] original description

Allen's Test (a.k.a. Allen's Maneuver:[edit | edit source]

The examiner flexes the patient’s elbows to 90 degrees while the shoulder is extended horizontally and rotated externally. The patient the rotates the head away from the side tested. A positive test is indicated by a disappearance of the radial pulse.

[11]

[12]

Diagnostic Values[edit | edit source]

Based on a cut-off of 6 seconds on the Allen’s test the sensitivity was 54.5%, specificity of 91.7%, and diagnostic accuracy of 78.5%. At a cut-off of 5 seconds diagnostic accuracy was maximal (79.6%), with a sensitivity of 75.8% and specificity of 81.7%; 100% sensitivity occurred at a cut-off of 3 seconds, with specificity of 27% and diagnostic accuracy of 52% [13].

The predictive value of a negative test is 0.8% and of a positive test is only 53% [14].

References[edit | edit source]

  1. ↑ 1.0 1.1 Allen E. Thromboangiitis obliterans: methods of diagnosis of chronic occlusive arterial lesions distal to the wrist with illustrative cases. The American Journal of the Medical Sciences. 1929;178(2):237-243.
  2. ↑ Asif M & Sarkar, P. Three-Digit Allen's Test. Annals of Thoracic Surgery. 2007; 84 (2):686-687.
  3. ↑ 3.0 3.1 3.2 3.3 Oettlé A, van Niekerk A, Boon J, Meiring J. Evaluation of Allen’s test in both arms and arteries of left and right-handed people. Surgical and Radiologic Anatomy. 2006;28(1):3-6.
  4. ↑ 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
  5. ↑ Adam J. Hansen. Reverse Radial Forearm Fascial Flap With Radial Artery Preservation. American Association for Hand Surgery 2007
  6. ↑ WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy. Geneva: World Health Organization; 2010. Annex I, Modified Allen test. Available from: https://www.ncbi.nlm.nih.gov/books/NBK138652/
  7. ↑ Woon C. Blood Supply to Hand - Hand - Orthobullets [Internet]. Orthobullets.com. 2018 [cited 14 July 2018]. Available from: https://www.orthobullets.com/hand/6007/blood-supply-to-hand
  8. ↑ 8.0 8.1 AnatomyZone. Upper Limb Arteries - Hand and Wrist - 3D Anatomy Tutorial [Internet]. 2018 [cited 14 July 2018]. Available from: https://www.youtube.com/watch?v=lRjF5wI_IqU
  9. ↑ 9.0 9.1 Asif M, Sarkar P. Three-Digit Allen’s Test. The Annals of Thoracic Surgery. 2007;84(2):686-687.
  10. ↑ Greenhow D. Incorrect Performance of Allenʼs Test—Ulnar-artery Flow Erroneously Presumed Inadequate. Anesthesiology. 1972;37(3):356-357.
  11. ↑ Physiotutors. Allen Test⎟Hand Vascularisation. Available from: https://www.youtube.com/watch?v=D1tJO0RW9UM
  12. ↑ The Student Physical Therapist. Allen's Test [Internet]. 2017 [cited 12 July 2018]. Available from: https://www.youtube.com/watch?time_continue=66&v=6M9MzzzpCek
  13. ↑ 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
  14. ↑ Husum B, Berthelsen P. Allen’s test and systolic arterial pressure in the thumb. British Journal of Anaesthesia. 1981;53(6):635-637.
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