The American Red Cross has declared a national blood crisis for only the second time in its history, warning that its supply has fallen to less than one day's worth of blood. The American Red Cross has declared only the second national blood supply crisis in its history, warning the U.S. has less than a one-day supply of type O blood. People battling cancer, especially those undergoing chemotherapy, use about one quarter of the nation's blood supply. All blood types are currently needed, but the Red Cross said there is a particular need for type O blood. "If we could just get three more donors at every single blood drive this summer, that would be enough to stop the shortage," said Kelly Isenor of the American Red Cross.