What is the purpose of the Allen test?

The purpose of the Allen test is to determine the patency of the radial and ulnar arteries. This is particularly important in assessing the blood supply to the hand before procedures such as arterial blood gas sampling or the insertion of an arterial line. During the test, pressure is applied to compress both the radial and ulnar arteries at the wrist. Once the pressure is released from one artery, observing the return of color to the hand indicates whether blood flow through that artery is adequate. This helps to ensure that there is sufficient collateral circulation before proceeding with any invasive procedures involving the radial artery.

Other options, such as examining the knee reflex or checking oxygen saturation, pertain to completely different assessments and not to the vascular evaluation that the Allen test provides. Blood pressure measurement is unrelated as well, focusing instead on systemic blood pressure rather than localized arterial occlusion and patency.