Why is there never enough
O Rh-negative blood?

While listening to the news driving home you hear an emergency appeal for "O-negative" blood donors. Your hospital transfusion service tells you to "go easy" on O Rh-negative blood. Familiar?

You wonder why there is never enough O Rh-negative blood, especially if you've been personally involved in the care of a patient where there wasn't enough of this blood.

I'll try to explain why, and suggest what you as a physician can do to prevent shortages of O Rh-negative blood.

Only 7 percent of Caucasians are O Rh-negative; approximately 3-4 percent of African-Americans and less than 1 percent of persons of Asian background are O Rh-negative. When these persons need blood, they have no choice but to get blood of their own type (except in times of severe shortage as described below). But because O Rh-negative packed red cells, the "universal donor" type, can be given to persons of any type in an emergency, this blood is used for much more than 7 percent of the population.

The commonest situation requiring use of O Rh-negative blood for non-O Rh-negative patients is hemorrhagic shock from trauma or sudden internal hemorrhage, when there is insufficient time to obtain a type and crossmatch. In situations like this, or where the recipient is O Rh-negative , one or two patients can easily deplete the entire community's reserves of O Rh-negative blood. If this were to happen, the next patient in similar need would be in severe jeopardy, and elective surgery for O Rh-negative patients needing blood would have to be postponed.

What can you do to ensure there is enough O Rh-negative blood?

First, minimize the situations where this blood is used for non-O Rh-negative patients. In an emergency, the knowledge that type-specific uncrossmatched blood can be provided within 10-15 minutes should eliminate many unnecessary requests for O Rh-negative blood. For patients who are issued unmatched O Rh-negative blood in a severe emergency (e.g., trauma cases), your hospital should have a system in place for rapid delivery of the patient's specimen to the blood bank for typing so you can switch to O Rh-positive or type-specific blood as soon as possible (there's an over 90 percent probability that an untyped patient will be other than O Rh-negative). As mentioned above, this can usually be done within 10-15 minutes.

Second, in a severely bleeding O Rh-negative male or a female beyond childbearing years , switch to O-positive red cells as soon as possible. Every hospital transfusion service should have a written policy stating when such a switch should be made (especially when O Rh-negative blood is in short supply). This is often stated in terms such as "Whenever a bleeding Rh-negative recipient requires more than 2-4 units of red cells in 'x' hours it is appropriate to switch to Rh-positive red cells." Provided that these patients do not have pre-existing Rh antibodies (rare today, since most persons at risk are Rh-negative women who since 1968 have been protected by receiving anti-D immunoglobulin during/after pregnancy), giving them Rh-positive red cells will not cause an acute hemolytic transfusion reaction. Antibodies will usually develop over a period of months, but by the time they reach levels sufficient to cause hemolysis most of the transfused Rh-positive red cells will have disappeared. And it is unlikely they will encounter a similar emergency needing Rh-positive cells in the future.

Working together we can minimize shortages of O Rh-negative blood that place patients in jeopardy. Being considerate of the community's blood supply is the best policy for all of us. At least until we've figured out how to convert all blood to O Rh-negative. Don't laugh. Research is underway to convert type A & B red cells to type O, but we're not there yet!

Reference:

Naiman JL. Bulletin of the Santa Clara County Medical Association. May, 1998.