Most UK and international cord blood banks, both public and private, process cord blood to reduce levels of the plasma and the red cells, and cryo-preserve the remaining buffy coat portion which contains mononuclear cells. This mononuclear cell fraction contains the critical CD34 positive stem cells. It is valid for cord blood storage banks to use volume reduction techniques as such units are clinically preferable to whole blood, red cell replete products. This is based on large cohorts of international data from respected and accredited transplant centres who use cord blood regularly as a therapeutic tool. The plasma and red cells in cord blood are not deemed to be useful clinically. By reducing the volume of the sample, while retaining the critical stem cells, it is possible to minimise the volume of cryoprotectant solution required in the freezing process. The cryoprotectant contains a substance called DMSO that can cause reactions in patients so it is sensible to reduce the volume as much as possible.
The reduction of red blood cell content is very important as it is well recognised that red blood cells burst or lyse during the freezing process. This results in release of free haemoglobin and red cell debris which can cause complications to patients at the time of infusion.
There are whole cord blood units in-store that was mostly banked before preference for volume reduction became a factor and some of these are used for transplantation if there is no better match available in the volume-reduced format. Under these circumstances, key worldwide organisations which issue standards of practice recommend washing the units to remove lysed red blood cell material to avoid clinical complications. However, this can result in the loss of some stem cells.
Information taken from the following sources:
The Joint Accreditation Committee-ISCT (Europe) & EBMT (JACIE) : The Hematopoietic Cellular Therapy Accreditation Manual 6th Edition which accompanies the FACT-JACIE International Standards for Hematopoietic Cellular Therapy Product Collection, Processing, and Administration.
The National Marrow Donor Program® (NMDP), ( USA)
Transfusion. 2012 Jan; 52(1): 207–208
The Circular of Information for the use of cellular therapy products (AABB publication) http://www.aabb.org/aabbcct/coi/Pages/default.aspx
Ballen et al. Biol Blood Marrow Transplant. 2015 Apr; 21(4): 688–695.