Before arterial blood gases are drawn, which test should be performed to assess arterial patency?

• A. CBC
• B. Chest X-ray
• C. EKG
• D. Allen's test

Answer: (D)

Evaluating arterial patency before arterial blood gas sampling from the radial artery hinges on ensuring the hand will still receive adequate blood supply if the radial artery is compromised. Allen's test checks the palmar collateral circulation by assessing whether the ulnar artery can sustain perfusion if the radial artery is occluded. In practice, you compress both arteries at the wrist while the patient makes a fist to blanch the hand, then release the ulnar artery. If color and perfusion return quickly, within about 5–15 seconds, the palmar arch is patent and it’s safe to proceed with radial ABG sampling. If color does not return promptly, radial access could cause ischemia, so another site should be used. The other tests—CBC, chest X-ray, and EKG—do not assess arterial patency or collateral circulation and serve different diagnostic purposes.