Despite potential risk, sometimes immediate transfusion is necessary, even for patients with red cell antibodies. In such cases transfusion service staff should alert the medical director, who can discuss options with clinical staff.
The medical director will generally talk to the staff attending the patient and indicate that, if possible, they should hold off transfusion. But if it is a case of massive bleeding where exsanguinating hemorrhage is likely, it is better to give some blood and monitor for a delayed hemolytic transfusion reaction than to let the patient bleed to death.
Transfusing when bleeding is brisk will result in much of the autologous and incompatible blood bleeding out, with the possibility of a delayed hemolytic reaction once the patient's antibody rebounds and destroys still present antigen-positive donor red cells.
Some transfusion services also try to minimize the risk of unmatched blood by typing their emergency supply of O Rh negative Red Blood Cells for the K antigen, since anti-K is a relatively common clinically significant antibody.