[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Clinical exam](https://durgical.com/en/clinical-exam/) › [Cardiovascular system](https://durgical.com/en/clinical-exam/#a-cardiovascular) › Allen test

[Clinical exam](https://durgical.com/en/clinical-exam/) · [Cardiovascular system](https://durgical.com/en/clinical-exam/#a-cardiovascular)

# Allen test

- Maneuver

Before puncturing the artery at the wrist, check that the hand's other artery can supply it on its own.

Updated 2026-11-01

**See it in 3D:** [Radial artery](https://durgical.com/en/anatomy/radial-artery/) · [Ulnar artery](https://durgical.com/en/anatomy/ulnar-artery/)

## Key points

- Tests ulnar collateral flow before puncturing or cannulating the radial artery.
- Compress both arteries, open the pale hand, release only the ulnar.
- Quick return of color = adequate ulnar flow; pale palm = choose another site.
- Limited sensitivity and specificity: Doppler is more objective.

## What it is

The modified Allen test checks whether the ulnar artery supplies enough blood to the hand while the radial artery is occluded. It is done before a radial arterial blood gas, an arterial line or use of the radial artery as a graft. It is a classic nursing safety check.

## The anatomy it tests

- The hand is supplied by two arteries, radial and ulnar, joined by the superficial (mainly ulnar) and deep (mainly radial) palmar arches.
- With complete arches the ulnar artery alone refills the whole hand in a few seconds.
- With incomplete collateral flow, injury or thrombosis of the radial artery can leave part of the hand ischemic.

## How to do it

- Place the patient's hand palm up and ask the patient to make a tight fist.
- Compress the radial and ulnar arteries at the wrist at the same time with thumbs or fingers.
- Ask the patient to open the hand without overextending the fingers: the palm should look pale.
- Release only the ulnar artery, keeping the radial occluded.
- Watch how long the pink color takes to return to the whole palm and fingers.
- Record the result; if the other hand is to be used, repeat there.

## What a positive result means

- Normal (negative Allen test, adequate collateral flow): color returns within a few seconds; most protocols use a cutoff between 5 and 10 seconds.
- Abnormal (positive): the palm stays pale; the ulnar artery does not compensate and another puncture site is chosen.
- A persistently cold or pale hand may reflect arterial disease, Raynaud phenomenon or vasospasm.

## Usefulness and limits

- It is subjective and its ability to predict ischemia is debated; Doppler ultrasound or pulse-oximeter plethysmography is more objective.
- Hyperextending the fingers or wrist blanches the palm and gives a false positive.
- It cannot be done if the patient cannot cooperate (unconscious); Doppler or oximetry is used instead.

## Test yourself

Think of the answer, then tap the question to see it.

## Which artery is released first in the modified Allen test?

The ulnar artery, with the radial still compressed, to see whether the ulnar alone perfuses the hand.

## What is done if the palm stays pale after the ulnar artery is released?

Collateral flow is considered inadequate and another site is chosen for the arterial puncture.

## Which technical error gives false positives in the Allen test?

Hyperextending the fingers or wrist when opening the hand, which blanches the palm even with blood flow.

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## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Radial artery](https://durgical.com/en/anatomy/radial-artery/)
- [Ulnar artery](https://durgical.com/en/anatomy/ulnar-artery/)

## Related

- [Peripheral pulses and the ankle–brachial index](https://durgical.com/en/clinical-exam/peripheral-pulses-and-the-ankle-brachial-index/)
- [Capillary refill time](https://durgical.com/en/clinical-exam/capillary-refill-time/)
- [Arterial pulse: rate, rhythm and amplitude](https://durgical.com/en/clinical-exam/arterial-pulse-rate-rhythm-and-amplitude/)

## Related conditions

- [Raynaud phenomenon](https://durgical.com/en/conditions/raynaud-phenomenon/)

[← All of the clinical exam](https://durgical.com/en/clinical-exam/)

Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.

Sources: [10.4 Blood Sampling - Clinical Nursing Skills | OpenStax](https://openstax.org/books/clinical-nursing-skills/pages/10-4-blood-sampling) (OpenStax (Rice University), 2024); [24.3 Nursing Assessment - Clinical Nursing Skills | OpenStax](https://openstax.org/books/clinical-nursing-skills/pages/24-3-nursing-assessment) (OpenStax (Rice University), 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/clinical-exam/allen-test/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/clinical-exam/allen-test/