In Allen's test, the arm is positioned with the shoulder and elbow both at 90 degrees, and the head is turned away; which finding constitutes a positive result?

• A. Shoulder 90° abduction and 90° elbow flexion; Turn head away; deep breath; radial pulse diminished
• B. Elbow 90° flexion; head toward; pulse stronger
• C. Seated. Shoulder 90° abduction and 90° elbow flexion. Turn head away, take a deep breath, and hold it. Check radial pulse. Positive is absent or diminished pulse
• D. Elbow extended; pulse unchanged

Answer: (C)

Allen's test checks whether the hand has adequate collateral blood flow through the palmar arches when one arterial path is occluded. In this setup, the positive result is when, after exposing the hand to the maneuver and releasing the tested artery, the radial pulse is absent or markedly diminished. That lack of pulse indicates insufficient collateral circulation to the hand, suggesting a potential vascular compromise. If the pulse returns normally, the collateral supply is adequate, and the test is considered negative.