View source for Allen's test

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  Caption        = Arteries of the hand|
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{{SK}} Allen test

==Overview==
In [[medicine]], Allen's test, is used to test blood supply to the hand. It is performed prior to [[radial artery|radial]] [[artery|arterial]] [[blood]] sampling or [[cannula]]tion.

==Historical Perspective==
It is named after [[Edgar Van Nuys Allen]].<ref>{{WhoNamedIt|synd|189}}</ref>

== The Allen's Test ==
# The hand is elevated and the patient/person is asked to make a fist for about 30 secs.
# Pressure is applied over the ulnar and the radial arteries so as to occlude both of them.
# Still elevated, the hand is then opened. It should appear blanched (pallor can be observed at the finger nails).
# Ulnar pressure is released and the color should return in 7 secs.

Inference: [[Ulnar artery]] supply to the hand is sufficient and it is safe to cannulate/prick the radial.

If color does not return or returns after 7 seconds, then the ulnar artery supply to the hand is not sufficient and the radial artery therefore cannot be safely pricked/cannulated.

== Anatomical Basis ==
The hand is normally supplied by blood from the ulnar and radial arteries. The arteries undergo [[anastomosis]] in the hand. Thus, if the blood supply from one of the arteries is cut off, the other artery can supply adequate blood to the hand. A minority of people lack this dual blood supply.

== Significance ==
An uncommon complication of radial arterial blood sampling / cannulation is disruption of the artery (obstruction by [[clot]]), placing the hand at risk of [[ischemia]]. Those people who lack the dual supply are at much greater risk of [[ischemia]]. The risk can be reduced by performing Allen's test beforehand. People who have a single blood supply in one hand often have a dual supply in the other, allowing the practitioner to take blood from the side with dual supply.

The utility of the Allen's test is questionable,<ref name="pmid11081899">{{cite journal |author=Jarvis MA, Jarvis CL, Jones PR, Spyt TJ |title=Reliability of Allen's test in selection of patients for radial artery harvest |journal=Ann. Thorac. Surg. |volume=70 |issue=4 |pages=1362–5 |year=2000 |month=October |pmid=11081899 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/S0003-4975(00)01551-4}}</ref> and no direct correlation with reduced ischemic complications of radial artery cannulation have ever been proven.  In 1983, Slogoff and colleagues reviewed 1,782 radial artery cannulations and found that 25% of them resulted in complete radial artery occlusion, without apparent adverse effects.<ref>Slogoff s, Keats AS, Arlund C.  On the safety of radial artery cannulation.  Anesthesiology 1983; 59:42-7</ref>  A number of reports have been published in which permanent ischemic sequelae occurred even in the presence of a normal Allen's test.<ref>Thompson SR, Hirschberg A: Allen's test re-examined. Crit Care Med 16:915, 1988</ref><ref>Wilkins RG: Radial artery cannulation and ischaemic damage: A review. Anaesthesia 40:896-899, 1985</ref>  In addition, the results of Allen's tests do not appear to correlate with  distal blood flow as demonstrated by fluorescein dye injections<ref>McGregor AD: The Allen test-an investigation of its accuracy by fluorescein angiography. J Hand Surg [Br] 12:82-85, 1987</ref> or photoplethysmography.<ref>Stead SW, Stirt JA: Assessment of digital blood flow and palmar collateral circulation. Int J Clin Monit Comput 2:29, 1985</ref>

Modifications to the test have been proposed to improve reliability.<ref name="pmid17643672">{{cite journal |author=Asif M, Sarkar PK |title=Three-digit Allen's test |journal=Ann. Thorac. Surg. |volume=84 |issue=2 |pages=686–7 |year=2007 |month=August |pmid=17643672 |doi=10.1016/j.athoracsur.2006.11.038 |url=http://linkinghub.elsevier.com/retrieve/pii/S0003-4975(06)02283-1}}</ref>

==References==
{{Reflist|2}}

{{Eponymous medical signs for circulatory and respiratory systems}}

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