Allen's test assesses patency of which artery?

• A. Patency of the radial artery
• B. Patency of the ulnar artery
• C. Tests for blood glucose
• D. Checks hand sensation

Answer: (B)

Allen's test looks at the hand's blood supply from the two arteries that form the palm's arches—the radial and the ulnar—and whether there is enough collateral flow via the ulnar artery if the radial path is blocked. Before using the radial artery for procedures, you want to know the ulnar artery can keep the hand well perfused. The test is done by occluding both arteries at the wrist, having the patient clench the fist to blanch, then releasing one artery to see if color returns promptly. A quick return of color indicates that the released artery is patent and can supply the hand. This is why the test assesses the patency of the ulnar artery in this context.