ABO blood group system roles in cell membrane integrity, cell adhesion, membrane transportation of molecules, and acting as receptors for extracellular ligands, and enzymes. ABO antigens are found having similar roles on epithelial cells as well as red blood cells. The ABO antigen is also expressed on the von Willebrand factor (vWF) glycoprotein, which participates in hemostasis (control of bleeding). In fact, having type O blood predisposes to bleeding, as 30% of the total genetic variation observed in plasma vWF is explained by the effect of the ABO blood group, and individuals with group O blood normally have significantly lower plasma levels of vWF
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?"