Southern California faces a critical shortage of the most common type of blood, Group O, Red Cross officials said. Dr. Carroll Spurling, executive director of the Red Cross' Southern California blood services, said the trouble results from a shortage before the holidays and a lack of donors over the Christmas and New Year's period. "The shortage of type O blood is not unusual at this time of the year," said Dr. Carol Bell of Culver City's Brotman Medical Center. It has been made worse by new medical tests to ensure that blood is free of hepatitis strains, Bell said. "If there is any doubt that the blood should be used, it is discarded," Bell said, adding that more than 5% of donated blood is being discarded.