Blood type represent contributions from both parents. A total of 36 human blood group systems and 346 antigens are now recognized by the International Society of Blood Transfusion (ISBT). The two most important ones are ABO and the Rh blood group systems; they determine someone's blood type (A, B, AB and O, with +, − or null denoting RhD status) for suitability in blood transfusion. A complete blood type would describe a full set of 30 substances on the surface of red blood cells, and an individual's blood type is one of many possible combinations of blood-group antigens. Across the 36 blood
Jehovah's Witnesses and blood transfusions who are Jehovah's Witness would not administer blood transfusions to fellow dedicated members. As to administering transfusions to non-members, "The Watchtower" stated that such a decision is "left to the Christian doctor's own conscience." In 1982, a "Watchtower" article declared that it would be wrong for a Witness to allow a leech to feed on his/her blood as part of a medical procedure, due to the sacredness of blood. In 1989 "The Watchtower" stated, "Each individual must decide" whether to accept hemodilution and autologous blood salvage (cell saver) procedures. In 1990, a brochure entitled "How Can Blood Save Your Life?"