Modified Allen test

The patient's hand is initially held high while the fist is clenched and both radial and ulnar arteries are compressed (A); this allows the blood to drain from the hand. The hand is then lowered (B) and the fist is opened (C). After pressure is released over the ulnar artery (D), color should return to the hand within six seconds, indicating a patent ulnar artery and an intact superficial palmar arch.