[6] Side effects include red blood cell breakdown, high blood potassium, infection, volume overload, lung injury, and allergic reactions such as anaphylaxis.

This is done to provide a final product with a very specific hematocrit (percentage of red cells) with type O red cells and type AB plasma to minimize the chance of complications.

When the recipient’s blood group is not known, particularly in pre-hospital transfusion, low-titer O universal donor whole blood (LTOWB) can be used; this requires that the donor plasma contains only low titers of anti-A and anti-B.

A centrifuge can be used in a "hard spin" which separates whole blood into plasma and red cells or a "soft spin" which separates it into plasma, buffy coat (used to make platelets), and red blood cells.

The third method is sedimentation: the blood simply sits overnight, and the red cells and plasma are separated by gravitational interactions, which is used predominantly in low-income countries.

Whole blood processing must be completed within 24 hours to minimize the warm storage of red cells in the unit.