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.
Allen's test is also performed prior to heart bypass surgery. The radial artery is occasionally used as a conduit for bypass surgery, and its patency lasts longer in comparison to the saphenous veins. Prior to heart bypass surgery, Allen's test is performed to assess the suitability of the radial artery to be used as a conduit. A result of less than 3 seconds is considered as good and suitable. A result of between 3-5 seconds is equivocal, whereas the radial artery will not be considered for grafting if the result is longer than 5 seconds.
The utility of the Allen's test is questionable, 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. A number of reports have been published in which permanent ischemic sequelae occurred even in the presence of a normal Allen's test. In addition, the results of Allen's tests do not appear to correlate with distal blood flow as demonstrated by fluorescein dye injections
Modifications to the test have been proposed to improve reliability.
Read more about this topic: Allen's Test
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