Allen test for patency of radial and ulnar arteries. A, Patient elevates hand and makes fist while examiner occludes radial and ulnar arteries. B, Patient extends fingers, and blanching of hand is seen. C, Radial artery alone is released, and color of hand returns to normal. D, In thrombosis of ulnar artery, test is positive (hand remains blanched) when this artery alone is released.