Clinical exam · Cardiovascular system
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 · Ulnar artery
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.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Peripheral pulses and the ankle–brachial index
- Capillary refill time
- Arterial pulse: rate, rhythm and amplitude
Related conditions
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 (OpenStax (Rice University), 2024); 24.3 Nursing Assessment - Clinical Nursing Skills | OpenStax (OpenStax (Rice University), 2024).
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Representative model, for educational purposes only.