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Must cord blood be processed before storage?

The earliest cord blood transplants were performed with whole cord blood. Thus, it is not absolutely necessary to process cord blood in order to save patient lives. There has never been a prospective randomized trial to compare transplant patient outcomes with whole cord blood versus processed cord blood.

Today almost all cord blood banks, both public and private, process cord blood before storage. The processing removes the plasma, so that the volume that goes into storage is reduced. The processing also removes the red blood cells, to avoid toxic effects from red cells that burst during freezing (see below). The final portion that is cryopreserved is called the "buffy coat"; it is the portion of the blood that holds both white blood cells and stem cells. 

Researchers consider it important to remove red blood cells before preserving cord blood stem cells, and we have a fact sheet on red blood cell depletion. Red blood cells are removed because they tend to burst during freezing, which releases iron from the hemoglobin, and the iron can be toxic to patients. The alternate to removing the red cells before freezing is to wash any broken cells out of the cord blood unit upon thaw, but this washing step causes some loss of valuable cells.