The Allen test is used to assess collateral blood flow within the hands, specifically testing for the presence of a complete palmar arch. Edgar Van Nuys Allen first described the test in 1929. Dr. Allen was a professor of medicine at the Mayo Clinic in Rochester, Minnesota, where he studied peripheral vascular disease. He served as a US Army Medical Corps colonel in World War II. He led a distinguished career that included the presidency of the American Heart Association and the receipt of the 1960 Lasker Award. In 1952, Irving Wright described a modified version of the Allen test that has since largely supplanted the original method. It is referred to as the modified Allen test (MAT). The MAT examines 1 hand at a time, in contrast to Allen's version, and can be used to assess either radial or ulnar arterial flow (See Video. Modified Allen Test).