Many parents these days are choosing to have their baby’s umbilical cord blood frozen and stored as a future source of stem cells. This article looks at the different ways in which blood and stem cell samples are stored.

The process of having your baby’s umbilical cord blood collected, processed in a laboratory and kept in frozen storage is a relatively new one. The idea is that the whole blood containing the stem cells or the extracted stem cells themselves are available for future use if the child needs any medical treatments which require them. Although some treatments such as those for sickle cell disease, leukemia and Hodgkin’s disease already use these cells, the idea is to also have a stock of compatible cells that can be used in treatments yet to be developed. Since the use of this type of cell for medical treatments is the subject of much current research, the likelihood of new treatments becoming available in the future is high. These future treatments have the potential to offer cures for diseases, injuries and conditions that are incurable today.

The collection and storage process starts just after birth when the umbilical cord blood collection kit supplied by the storage company is used by one of the medical professionals to safely and painlessly collect the blood from the cord. This sample is then transported to the storage company’s laboratory for processing. Some companies will extract the stem cells from the cord blood before freezing the sample, whereas others freeze the whole blood.

Liquid Phase Nitrogen

The sample is frozen in a storage tank which is cooled by liquid nitrogen at around minus 190 degrees Celsius. This extremely low temperature can preserve the quality of the sample for many years. There are, however, important storage tank design factors to take into account when deciding which method of storage to choose. The two main types of tank both use liquid nitrogen for freezing, but use it in different ways. The oldest method uses liquid nitrogen in its liquid phase to freeze the sample and keep it at the required temperature for storage. The important thing to remember is that there are usually also other samples from other individuals in the same storage tank. The liquid phase nature of the nitrogen in the tank means that there is a possible risk of contamination of samples by infectious disease particles if there was one or more infected samples in the tank. The liquid nitrogen can carry infectious particles, such as viruses, between samples. There is evidence that transmission of Hepatitis B virus between samples has occurred while the samples were stored in liquid phase nitrogen.*

Vapour Phase Nitrogen

The other design of storage tank also uses liquid nitrogen, but it is used in a different way. The liquid nitrogen is confined to the walls of the storage container, and only vapour phase nitrogen comes into contact with the samples. This means that any infectious particles present in a sample could not be carried to other samples to cause contamination. In the past, concerns were voiced about the vapour phase nitrogen’s ability to maintain the correct storage temperature when the tank was opened for access. Design improvements now mean that a constant temperature can be maintained in this design of storage tank.

*Tedder R., M. Zuckerman, A. Goldstone, A. Hawkins, A. Fielding, E. Briggs, D. Irwin, S. Blair, A. Gorman, K. Patterson, D. Linch, J. Heptonstall, and N. Brink. 1995. Hepatitis B transmission from contaminated cryopreservation tank. Lancet 346: 137-140.