Three-digit Allen's test.

Hand ischemia after radial artery intervention remains a rare but serious complication. Allen's test is widely used to assess the adequacy of ulnar collateral circulation to the hand. There have been documented cases of hand ischemia after radial artery intervention even with a negative test. We describe a modification of Allen's test based on the anatomy of the radial artery branches that could potentially decrease the number of false negative tests.