There has been interest in the use of whole blood for immediate resuscitation of trauma patients. Type O blood is used since the red cells will not be affected by anti-A or anti-B in the recipient. However, it is not entirely risk free.
While O Rh-negative blood would be preferred, O Rh-positive blood is used since it is more readily available.
Usually IgM antibodies are low-titer. For a antibody to be high-titer, it must usually be IgG.
If high-titer O whole blood is transfused into a type A, B or AB patient, then there is a high risk of a hemolytic transfusion reaction.
There is some variation in the definition of low titer. It may range <= 1:50 to <= 1:200 for whole blood.
Complications:
(1) hemolysis related due to anti-A, anti-B or anti-A,B in the plasma if the recipient is type A, B or AB
(2) sensitization to Rh antigen if the recipient is Rh-negative and the donor is Rh-positive
(3) interference with back typing in blood compatibility testing until anti-A, anti-B and anti-A,B cleared
