Allen Test

The Allen Test for Blood Flow

What is an Allent Test?

The Allen test is a simple medical procedure used to assess the adequacy of blood flow to the hand and to evaluate the patency of the radial and ulnar arteries. It is commonly performed before certain procedures, such as arterial blood gas sampling or radial artery catheterization, to ensure that the hand’s blood supply is adequate and to minimize the risk of complications.

The test was first described by Edgar V. Allen in 1929 as a means of assessing the collateral circulation in the hand. The collateral circulation refers to the network of blood vessels that provide alternative pathways for blood flow when the primary blood vessels are blocked or compromised.

What is a Modified Allen Test?

The modified Allen test, also known as the modified Allen’s test, is a medical procedure used to assess the adequacy of collateral blood flow to the hand before certain procedures. It is a variation of the original Allen test and is often performed when the radial artery is not easily accessible or in cases where the ulnar artery is the preferred site for arterial cannulation.

The purpose of the modified Allen test is to determine if the ulnar artery is providing sufficient blood flow to the hand before temporarily occluding it for procedures like arterial line placement or cardiac catheterization. By assessing the collateral circulation, healthcare providers can ensure that the hand will continue to receive adequate blood supply even if the ulnar artery is compromised during the procedure.

  • This Allen test was first defined in 1929 by Edgar V. Allen.
  • It is a non-invasive assessment of the hand’s vascular patency in thromboangitis obliterans patients.
  • Since then, the Modified Allen test (MAT) has been developed from this Allen test.
  • By simultaneously squeezing one artery in each hand, the examiner (therapist) performs the standard Allen’s test on both hands.
  • The Modified Allen Test (MAT) is a useful test for determining if collateral circulation is sufficient, but it requires assessing each hand independently.
  • The Allen test is a first-line standard procedure for determining the hand’s arterial blood flow.
  • When planning intravascular access to the radial artery or choosing patients for radial artery harvesting, such as for coronary artery bypass grafting or forearm flap elevation, the Allen test is performed.
  • The Allen test is a step in the diagnostic process for upper limb vascular anomalies such as thoracic outlet syndrome (TOS).
  • One potential cause of thoracic outlet syndrome (TOS), and more specifically vascular thoracic outlet syndrome (TOS), is the compression of the subclavian artery/vein by muscle bodies at the scalene muscle, which is susceptible to muscular hypertrophy.

Clinically Relevant Anatomy of the Hand

  • The radial and ulnar arteries provide the majority of the hand’s complex and large circulatory network.
  • The wrist joint separates into a superficial branch that contributes to the superficial palmar arch, and the radial artery travels through the brachioradialis and flexor carpi radialis muscles of the forearm.
  • The deep palmar arch is formed by the dorsal and deep crossing of the other radial artery into the tendons of the anatomic snuffbox.
  • The ulnar artery enters Guyon’s canal near the wrist joint, where it is divided into a deep palmar branch and a superficial palmar branch. The ulnar artery is located below the flexor carpi ulnaris of the forearm.
  • While the deep branch contributes to the deep palmar arch, the superficial palmar branch creates the superficial palmar arch.
  • The blood flow for the deep and superficial palmar arches, which make up the hand’s blood supply, is ensured by one of the arteries being blocked since the radial and ulnar arteries share an anastomosis.

What is the Allen Test for Blood Flow used for?

The integrity of the radial and ulnar arteries is assessed using the Allen test.
This Allen test is too common to specify which artery supplies the major blood supply to the hand.

What is the procedure of the Allen Test for Blood Flow?

  • Position of the patient=Seating position
  • The patient is instructed to open and close their hands multiple times as quickly as they can squeezing them forcefully.
  • The radial and ulnar arteries are compressed by the examiner’s thumb and index finger.
  • Alternately, the examiner (therapist) may use both hands, placing the fingers on the back of the arm for support and the thumb over each artery to compress the artery.
  • The patient then opens the hand while the arteries are still under pressure.
  • A single artery is examined by releasing pressure over it and observing how the hand flushes.
  • After that, another artery is examined in the same way.
  • Comparison testing should be done on both hands.
  • This examination identifies which artery supplies the majority of the blood to the hand and the state of the radial and ulnar arteries.

Diagnostic Values and Interpretation of the Allen Test for Blood Flow:

  • In the Allen test, palmar blanching is produced by applying digital compaction to the ulnar and radial arteries at the level of the proximal wrist joint notch. After dismissing the contraction on any artery, hypermedia also develops in the unaffected state.
  • The restoration of color to the hand within an appropriate amount of time is a sign of healthy collateral circulation.
  • The Allen Test has a sensitivity of 54.5%.
  • The Allen Test’s specificity is 91.7%.
  • The Allen Test has a diagnostic accuracy of 78.5%.
  • The cutoff for this outcome was 6 seconds.
  • The Allen Test’s maximum diagnostic accuracy is 79.6%, and its sensitivity is 75.8%.
  • Allen Test Specificity = 81.7%; this result is at the 5-second threshold.
  • Allen Test Sensitivity = 100%
  • Allen Test Specificity = 27%
  • Allen Test diagnostic precision: 52%
  • This effect is at the cutoff of 3 seconds.


What is Allen’s blood flow test?

The Allen test can be used to evaluate collateral blood flow to the hands, typically prior to a procedure that may disturb blood flow in the radial or ulnar arteries.

Is Allen’s test safe?

Conclusions: The Allen test is a reliable and valid screening procedure for measuring hand circulation.

What happens if Allen’s test is positive?

A positive result on the modified Allen test: If the hand flushes within 5–15 seconds, this suggests that the ulnar artery is receiving enough blood flow and is considered a positive result.

What does a positive Allen’s test mean?

A positive Allen test indicates that the patient’s dual blood supply to the hand may be sufficient.

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