Allen test

Originally devised in 1929 by Edgar Van Nuys Allen (1900-1961) to detect arterial occlusion in the context of thromboangiitis obliterans (Buerger’s disease). The test has since been widely adopted in contexts including pre-procedural screening for radial artery cannulation, arterial blood gas sampling, and radial artery harvest for coronary bypass surgery or forearm flap procedures.

The more commonly used Modified Allen Test (MAT) was proposed by Irving Sherwood Wright (1901-1997) in 1952, shifting the manoeuvre from a bilateral hand comparison to a unilateral hand assessment, which better isolates vascular integrity per limb and improves usability in clinical scenarios.

Clinical Use and Interpretation

The Allen test remains a common screening tool for assessing the adequacy of collateral perfusion from the ulnar artery before procedures that may compromise radial artery flow.

• A normal (positive) result is indicated by prompt return of hand colour (typically within 5 to 10 seconds) following release of one artery.
• A delayed or absent colour return is considered abnormal (negative), suggesting poor collateral supply and increased risk of ischaemia should the tested artery be compromised.

However, the diagnostic accuracy and clinical utility of the Allen test have been the subject of ongoing debate. Systematic reviews and meta-analyses report a sensitivity ranging from 66–78% and specificity from 81–97%, depending on the technique and timing criteria used. Studies have shown that even with a “normal” test, radial artery occlusion or ischaemic complications can still occur. Furthermore, some ischaemic complications have been documented despite an adequate test result, and conversely, many patients with “abnormal” results undergo procedures without adverse effects.

Variations and Evolving Standards

Several modifications and adjunctive techniques have been proposed to improve the objectivity and reproducibility of the test. These include:

• Three-digit compression techniques for better arterial occlusion control
• Pulse oximetry and plethysmography to reduce reliance on visual pallor assessment
• Doppler ultrasonography as the current gold standard for evaluating hand arterial flow and palmar arch completeness

Despite its limitations, the test persists in clinical routines largely due to its simplicity and zero cost. Yet, modern guidelines increasingly recommend Doppler-based assessment, particularly when planning radial artery harvesting for CABG, where objective evidence of complete arch circulation is preferred.

Typical Use Today

• Routinely used before radial artery cannulation or harvest
• Supplemented or replaced by Doppler ultrasound in high-stakes procedures
• Not universally predictive of ischaemic risk but still used as a screening threshold

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History

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Associated Persons

• Edgar Van Nuys Allen (1900-1961)
• Irving Sherwood Wright (1901-1997)

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Alternative names

• Allen’s test
• Modified Allen Test

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Controversies

Did they first describe or popularise or plagiarise?

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References

Historical references

• Allen EV. Thromboangiitis obliterans: methods of diagnosis of chronic occlusive arterial lesions distal to the wrist with illustrative cases. Am J Med Sci 1929;178(2): 237-244
• Wright IS. The Allen Test. In: Vascular diseases in clinical practice (2e) 1952: 38-39
• Ejrup B, Fischer B, Wright IS. Clinical evaluation of blood flow to the hand. The false-positive Allen test. Circulation. 1966 May;33(5):778-80.

Eponymous term review

• Baumann DP. The specificity of the Allen test in obliterative vascular disease. Angiology. 1954 Feb;5(1):36-8
• Cable DG, Mullany CJ, Schaff HV. The Allen test. Ann Thorac Surg. 1999 Mar;67(3):876-7.
• Jarvis MA, Jarvis CL, Jones PR, Spyt TJ. Reliability of Allen’s test in selection of patients for radial artery harvest. Ann Thorac Surg. 2000 Oct;70(4):1362-5.
• 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.
• Asif M, Sarkar PK. Three-digit Allen’s test. Ann Thorac Surg. 2007 Aug;84(2):686-7.
• 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. 
• Bertrand OF, Carey PC, Gilchrist IC. Allen or no Allen: that is the question! J Am Coll Cardiol. 2014 May 13;63(18):1842-4. 
• Romeu-Bordas Ó, Ballesteros-Peña S. Validez y fiabilidad del test modificado de Allen: una revisión sistemática y metanálisis [Reliability and validity of the modified Allen test: a systematic review and metanalysis]. Emergencias. 2017 Abr;29(2):126-135.
• Elwali A, Moussavi Z. The modified Allen test and a novel objective screening algorithm for hand collateral circulation using differential photoplethysmography for preoperative assessment: a pilot study. J Med Eng Technol. 2020 Feb;44(2):82-93.
• Golamari R, Gilchrist IC. Collateral Circulation Testing of the Hand- Is it Relevant Now? A Narrative Review. Am J Med Sci. 2021 Jun;361(6):702-710.