Allen Test Steps

The Allen Test, also known as Fist Closure Test, is a quick bedside examination used to assess the patency of the radial and ulnar arteries and the adequacy of the palmar arch circulation. It is especially important before procedures such as radial artery cannulation, arterial blood sampling, or radial artery harvest for coronary artery bypass grafting (CABG).

The original Allen’s test was described in 1929 by Edgar Van Nuys Allen who was a professor of medicine at the Mayo Clinic in Rochester, Minnesota (1900-1961). Then in 1952, Irving Wright described a modified Allen test that examines one hand at a time, in contrast to original Allen’s test, and can be used to assess either radial or ulnar arterial flow.

The Allen Test is performed to:

• Assess hand circulation before arterial line insertion.
• Evaluate collateral flow before radial artery harvesting for CABG.
• Check perfusion in cases of hand trauma or vascular injury.

How do you perform the Allens test?

The following steps describe the Modified Allen’s Test:

1. The patient is seated with the elbow flexed and forearm supinated, and raises his or her arm above the horizontal plane.
2. The examiner grasps the patient’s wrist and applies finger pressure to block the vascular supply from the radial and ulnar arteries.
3. The patient then makes a fist three to four times so as to force the venous blood out of the hand via the posterior veins.
4. After 1 minute, the patient lets the arm hang down and opens the now pale hand.
5. The examiner now releases compression, first from one artery then from the other.
6. This procedure is repeated with the radial artery released and compression on the ulnar artery maintained.

See Also: Flexor Tendon Injury of the Hand

The Original Allen test steps are as following:

1. The patient is asking to make a tightly fist with both hands simultaneously and keep this position for about 1 minute.
2. The examiner then applies a continuous pressure over the radial artery of the both hands to obstruct them.
3. The patient is then asked to release his hands rapidly.
4. The examiner observes the color changing of both hands (The pallor color should be quickly diminished and the hands and fingers restore the normal color.
5. The Allen test is repeated with the ulnar arteries.

What does a positive Allen Test mean?

Normal filling time is usually less than 5 seconds ( Rapid, uniform reddening of the hand in the areas supplied by the respective arteries).

If the return of color to the palm is significantly prolonged after the release of either artery, the examiner should conclude that perfusion from that artery is reduced (Negative Allen Test).

• A positive Allen test means that the patient may have an adequate dual blood supply to the hand (Normal filling time).
• A negative Allen test shows the patient may not have adequate dual blood supply (prolonged filling time) .

Sensitivity & Specificity

One study by Mika Kohonen ¹ found that the Allen’s test is a good and valid screening test for the circulation of the hand:

• Sensitivity: 73.2%
• Specificity: 97.1%

The Modified Allen Test has been evaluated for its diagnostic reliability using Doppler ultrasonography as the reference standard.

• Validity: The MAT demonstrated significant differences between patients with no flow compared to those with increased, decreased, or reversed flow patterns (p < 0.02). However, no significant differences were found between the decreased, increased, and reversed flow groups (p > 0.4298).
• Specificity:
  • Ulnar artery: 97.1%
  • Superficial palmar branch of the radial artery: 96.6%
  • Dorsal digital thumb artery: 97.1%
• Sensitivity:
  • Ulnar artery: 66.7%
  • Superficial palmar branch of the radial artery: 28.6%
  • Dorsal digital thumb artery: 100%
• Likelihood Ratios:
  • Positive: Ulnar artery 23, superficial palmar branch of RA 8.41, dorsal digital thumb artery 34.48
  • Negative: Ulnar artery 0.34, superficial palmar branch of RA 0.74, dorsal digital thumb artery 0.2

These findings indicate that the Modified Allen Test shows high specificity but variable sensitivity depending on the artery assessed. In particular, the test is most reliable when evaluating the dorsal digital thumb artery, where both specificity and sensitivity are strong.

Notes

Additional tools can be used to make Allen test more accurate, such as digital plethysmography, duplex ultrasonography with dynamic testing, and pulse oximetry (often with the sensor placed on the thumb tip).

The use of pulse oximetry while performing the Allen test is the easiest of these methods. The technique involves placing a pulse oximeter on the thumb before compression to get a baseline saturation and waveform. The examiner will then compress both radial and ulnar arteries until the waveform disappears and the oxygen saturation falls to zero. The pressure on the ulnar artery is then released. The waveform and the saturation are recorded. If these values are consistent with the baseline, it implies good collateral flow.

Similar test can be done in the fingers to assess the digital artery flow (Finger Allen test).

The vascular supply to the hand is important to assess before performing a procedure that might injure one of the arteries, such as inserting an arterial line into the radial artery or surgically approaching the scaphoid tubercle from its volar aspect.

In about 80% of normal individuals, the ulnar artery predominates over the radial artery. However, both arteries should be able to perfuse the hand in the majority of individuals.

Finger Allen test

In this case, the examiner observes the normal resting color of the finger in question and has the patient exsanguinate it by flexing the finger tightly.

The examiner then obstructs both digital arteries by compressing at both sides at the base of the finger.

Because the digital arteries are closer to the volar than the dorsal surface of the fingers, the examiner’s thumbs should be positioned to compress from the volar surface. The patient is then instructed to extend the finger.

The examiner then releases compression from one of the digital arteries and observes the time required for normal color to return to the finger.

As with the Allen’s test of the hand, the Finger Allen test is then repeated for the other digital artery so that the relative contributions of the two vessels can be compared.

Related Anatomy

The radial and ulnar artery originates from the Brachial artery at the at the level of the radial neck.

Radial artery:

• Initially it runs on the pronator teres, deep to the brachioradialis muscle, and continues to the wrist between this muscle and the FCR
• Forearm branches of the radial artery include the recurrent radial (which anastomoses with radial collateral artery) and muscular branches.
• At the wrist, the radial artery reaches the dorsum of the carpus by passing between the flexor carpi radialis (FCR) and the Abductor pollicis longus (APL) and Extensor pollicis brevis (EPB) tendons (snuffbox).
• Before that, it gives off a superficial palmar branch that communicates with the superficial arch (ulnar artery).
• It forms the deep palmar arch in the hand.
• The dorsal carpal branch of the radial artery enters the scaphoid dorsally and distally.

Ulnar artery:

• Ulnar artery is larger than the radial artery.
• It’s covered by the superficial flexors proximally (between Flexor Digitorum Superficialis FDS and Flexor Digitorum Profundus FDP).
• Distally the artery lies on the FDP between the tendons of the FCU and FDS.
• Forearm branches include the anterior and posterior recurrent ulnar (which anastomose with inferior and superior ulnar collateral arteries, respectively), the common interosseous (with anterior and posterior branches), and several muscular and nutrient arteries.
• At the wrist, ulnar artery lies on the Transverse Carpal Ligament.
• Ulnar artery gives off a deep palmar branch (which anastomoses with the deep arch) and then forms the superficial palmar arch.

Digital arteries arise from superficial palmar arch and run dorsal to digital nerves.

References

1. Allen EV. Thrombo-Angiitis Obliterans. Bull N Y Acad Med. 1942 Mar;18(3):165-89. PMID: 19312256; PMCID: PMC1933752.
2. Zisquit J, Velasquez J, Nedeff N. Allen Test. [Updated 2022 Sep 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: PubMed
3. Kohonen M, Teerenhovi O, Terho T, Laurikka J, Tarkka M. Is the Allen test reliable enough? Eur J Cardiothorac Surg. 2007 Dec;32(6):902-5. doi: 10.1016/j.ejcts.2007.08.017. Epub 2007 Sep 21. PMID: 17889550. PubMed
4. WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy. Geneva: World Health Organization; 2010. Annex I, Modified Allen test. Available from: PubMed
5. Ruengsakulrach P, Brooks M, Hare DL, Gordon I, Buxton BF. Preoperative assessment of hand circulation by means of Doppler ultrasonography and the modified Allen test. J Thorac Cardiovasc Surg. 2001 Mar;121(3):526-31. doi: 10.1067/mtc.2001.112468. PMID: 11241088. PubMed
6. Habib J, Baetz L, Satiani B. Assessment of collateral circulation to the hand prior to radial artery harvest. Vasc Med. 2012 Oct;17(5):352-61.
7. Onieal M-E: The hand: Examination and diagnosis, American Society for Surgery of the Hand, 3rd ed. New York: Churchill Livingstone, 1990.
8. Clinical Tests for the Musculoskeletal System 3rd Edition.
9. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.
10. Ronald McRae – Clinical Orthopaedic Examination 6th Edition Book.
11. Millers Review of Orthopaedics -7th Edition Book.