The Allen Test and Modified Allen Test assess visible hand reperfusion after temporary occlusion of radial and ulnar arterial flow. They are used as screening tools for hand collateral circulation, especially before procedures involving the radial artery. However, literature has questioned whether Allen testing reliably identifies collateral circulation problems, so abnormal or uncertain findings should not be used in isolation.
A client is being assessed before a procedure, vascular screen or upper-limb evaluation where hand circulation is relevant. You need to understand whether the hand reperfuses normally after temporary arterial occlusion.
The Allen Test can provide a quick visual screen of palmar circulation. However, it should be treated as a screening observation, not a definitive vascular diagnostic test.
Test name: Allen Test
Also known as: Modified Allen Test
Body region: Hand, radial artery, ulnar artery, palmar arch
Purpose: Screen visible collateral circulation to the hand
Positive or abnormal finding: Delayed, absent or clearly asymmetrical hand reperfusion after release of one artery
Negative or normal finding: Prompt return of colour after artery release
Best used with: Vascular history, pulse assessment, capillary refill, symptom screen and referral when indicated
Key limitation: It has questioned reliability and should not be used as a stand-alone clearance test
The Allen Test assesses hand reperfusion after temporary occlusion of the radial and ulnar arteries. The client opens and closes the hand to drain colour, both arteries are compressed, and one artery is released to observe return of blood flow.
The Modified Allen Test is commonly used clinically and is often discussed before radial artery procedures, arterial blood gas sampling or catheterisation.
The test is used to screen the adequacy of collateral circulation in the hand. It may be relevant before radial artery procedures or when vascular contribution to hand symptoms is being considered.
It assesses visible reperfusion of the hand after release of arterial compression. It does not directly measure blood flow volume, arterial diameter, oxygenation or vascular pathology.
This test may be useful when professionals need a quick hand circulation screen, particularly before radial artery access or when vascular symptoms are present.
Use when hand vascular screening is relevant and temporary artery compression is appropriate.
Use caution with known vascular disease, severe hand pain, acute ischaemic symptoms, wounds, Raynaud’s-type symptoms, recent vascular surgery, abnormal pulses, colour change or coldness. Abnormal vascular findings require appropriate medical assessment.
Observation space
Timer
Measurz recording workflow
Optional pulse oximetry or Doppler if available in the clinical context
Optional referral notes
Ask the client to sit with the hand visible and relaxed.
The hand is elevated slightly or held comfortably at chest level.
Sit or stand facing the palm.
Locate and compress the radial and ulnar arteries at the wrist.
Maintain consistent arterial compression without excessive pressure.
Ask the client to open and close the hand several times, then hold it open. Compress both arteries. Release one artery and observe colour return. Repeat for the other artery if needed.
Ask the client to report pain, numbness, coldness, dizziness or discomfort.
Delayed, absent or clearly asymmetrical return of colour after release of one artery.
Prompt return of colour after artery release.
Stop if pain, numbness, colour change, distress or vascular symptoms occur.
Do not maintain arterial compression longer than needed. Do not treat the test as a definitive vascular clearance tool.
An abnormal Allen Test may suggest delayed hand reperfusion through the released artery or inadequate collateral circulation. It should prompt caution and further assessment rather than a definitive conclusion.
A normal Allen Test suggests visible reperfusion occurred under test conditions. It does not guarantee vascular safety for procedures and should not override vascular history, symptoms or clinician judgement.
Evidence has questioned the diagnostic validity of the Allen Test and Modified Allen Test. A review on collateral circulation testing stated that neither Allen’s test nor the plethysmography-based Barbeau test adequately and reliably tests collateral circulation before radial artery procedures.
Condition or presentation: adequacy of collateral hand circulation
Population: people being screened before radial artery intervention or vascular procedures
Test variation: Allen Test or Modified Allen Test
Reference standard: variable across studies, including Doppler or other flow measures
Sensitivity: not reliably established for all settings
Specificity: not reliably established for all settings
Positive likelihood ratio: not consistently available
Negative likelihood ratio: not consistently available
Key limitations: visual interpretation, variable timing thresholds, compression technique, hand temperature, vascular anatomy differences and inconsistent reference standards
A Modified Allen Test study described its clinical purpose as assessing collateral circulation in the hand but also reflects that test performance is dependent on protocol and population.
Reliability depends on compression technique, timing, hand temperature, lighting, skin tone, client cooperation and interpretation of colour return.
Because validity is debated, abnormal, uncertain or clinically important vascular findings should be interpreted with vascular history and appropriate objective testing when needed.
Common errors include not fully compressing both arteries, compressing for too long, inconsistent timing, judging colour return poorly, ignoring symptoms and using a normal test as full procedural clearance.
Limitations include visual subjectivity, hand temperature effects, vascular anatomy variation and limited reliability.
Use the Allen Test as a screening observation, not as a definitive vascular diagnostic test. Record timing, symptoms and colour return clearly.
Record test name, side tested, artery released, colour return time, normal/abnormal/unclear result, symptoms, hand temperature if relevant, pulse findings, comparison side, confidence in result and referral recommendation.
Add vascular symptoms such as coldness, colour change, numbness, pain, swelling or history of vascular disease.
Wrist Tinel’s Test
Phalen’s Test
Grip Strength Test
Upper Limb Tension Tests
Arm Squeeze Test
Cervical ROM Tests
Thoracic Outlet Tests
Vascular Screen
It assesses visible hand reperfusion after temporary radial and ulnar artery compression.
Delayed, absent or clearly asymmetrical return of hand colour after artery release.
No. It suggests visible reperfusion under test conditions but does not fully clear vascular risk.
Evidence has questioned whether it reliably identifies collateral circulation problems.
Record side, artery released, colour return time, symptoms, comparison side and whether referral or further vascular testing is needed.
The Allen Test screens visible hand reperfusion.
It is not a definitive vascular diagnostic test.
Timing, artery released and symptoms must be recorded.
Evidence questions its reliability as a stand-alone clearance tool.
Measurz should capture colour return, symptoms, side and referral reasoning.
Jarvis, M. A., Jarvis, C. L., Jones, P. R., & Spyt, T. J. (2020). Collateral circulation testing of the hand: Is it relevant now? The American Journal of the Medical Sciences.
Kumar, A., Choudhary, N., & colleagues. (2020). Assessment of collateral hand circulation by modified Allen’s test in normal Indian subjects and elderly population. Journal of Clinical Orthopaedics and Trauma.
