In 1972, Cook County Hospital became the first hospital to use an all frozen blood banking system. This novel concept had already been tested in the Vietnam War by Lieutenant Commander Gerald S. Moss at the Navy Station Hospital in DaNang, Vietnam. Units of Group O and Rh, Kell, and Duffy negative blood were collected in acid citrate dextrose solution in Boston.

The red cells were separated from plasma and washed to remove anti-A and anti-B isoagglutinins, platelets, clotting factors, and bacteria and viruses. They were then placed in a specially designed freezing bag and glycerolized with a special solution of sugars to maintain osmotic equilibrium, and ethylenediaminetetraacetic acid (Na₂EDTA) to prevent development of Coombs-positive red cells. After mixing for ten minutes the bags were stored in a freezer at -80°C. The units were air transported to DaNang in polystyrene containers packed with dry ice.

Thus, large quantities of O negative red cells were available when required and blood components were not wasted since they were selectively administered only when indicated.