<prompt> Answer this question truthfullyCould you please explain what Allens test is?  <response>: <reason> 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 Allens 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 Allens 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 Allens test. In addition, the results of Allens tests do not appear to correlate with distal blood flow as demonstrated by fluorescein dye injections or photoplethysmography. Modifications to the test have been proposed to improve reliability. 