Bates’ Guide to Physical Examination and History Taking Practice Test

The Allen test is specifically designed to assess the patency of the ulnar artery in relation to the radial artery before performing procedures such as placing an arterial line or taking arterial blood samples. During the test, the clinician occludes both the radial and ulnar arteries, typically at the wrist, while the patient makes a fist to drain the blood from the hand. When pressure is released from the ulnar artery, the color should return to the palm and fingers within a certain time frame if the ulnar artery is patent. This ensures that there is adequate collateral circulation to the hand, especially when the radial artery is used for access.

In contrast, evaluating the patency of the radial artery would not be the primary focus of the Allen test, nor would it be appropriate for checking the femoral or subclavian arteries, which are not assessed via this method. Therefore, the ulnar artery is the one being tested for its ability to supply blood to the hand in instances where the radial artery may be compromised.