A low supply of O-negative blood has brought a plea ahead of a blood drive being held by Blood Assurance at Covenant Academy this Saturday.The call for blood comes following several traumatic accidents that were treated at member hospitals, leaving reserves, especially of O-negative blood, at dangerously low levels. Blood Assurance is the sole supplier of blood for Saint Thomas River Park Hospital and many other hospitals throughout Tennessee, Georgia and Virginia.O-negative is the universal blood type, meaning all patients in area hospitals and in trauma situations can receive it.Approximately 38 percent of the nation’s population is able to donate. Of those, 10 percent actually give blood.