When is an Allen test performed?

The Allen test is performed before an arterial puncture to evaluate the adequacy of blood circulation in the hand. Specifically, it assesses the collateral circulation of the radial and ulnar arteries. By occluding both the radial and ulnar arteries and then releasing one to observe blood flow, clinicians can determine whether the arteries are sufficient for potential arterial puncture. This is important because if one artery is not functioning well, it may lead to complications or inadequate blood supply if it is the only vessel supplying the hand during a procedure such as arterial blood gas sampling. This preventive measure helps ensure patient safety and the success of the procedure.