Umbilical cord blood, the residual blood remaining in the placenta and umbilical cord after birth, is a rich source of hematopoietic stem cells (HSCs). These stem cells are immature cells capable of developing into all types of blood cells, including red blood cells, white blood cells, and platelets. Cord blood banking preserves these cells for potential medical use, particularly for treating various blood disorders and immune system diseases. HSCs from cord blood are used in transplantation to replace a patient’s unhealthy blood-forming system with a new, healthy one. This is a standard treatment for conditions like leukemia, lymphoma, and certain genetic disorders. The viability of a stored unit depends on the number of stem cells it contains, not the total volume collected.
Defining the Usable Stem Cell Threshold
The required amount of cord blood is determined by cell count, not the physical volume collected. The most important metrics are the Total Nucleated Cell (TNC) count and the CD34+ stem cell count. The TNC count measures all nucleated cells, while the CD34+ count identifies the specific population of hematopoietic stem and progenitor cells.
A successful transplant requires infusing a sufficient dose of these cells, calculated based on the recipient’s body weight. For allogeneic transplantation, a standard minimum threshold is often cited as 2.5 x 10^7 TNCs per kilogram of recipient weight. Guidelines also suggest a minimum of 1.5 x 10^5 CD34+ cells per kilogram before cryopreservation.
Since dosage is weight-dependent, a single unit is usually sufficient for a child but rarely contains enough cells to treat a large adult. Banks often aim for a collection volume of at least 40 to 50 milliliters, which is an estimate of the volume needed to achieve the required cell counts. Ultimately, the laboratory analysis of the TNC and CD34+ counts determines the unit’s clinical utility.
The Umbilical Cord Blood Collection Procedure
The collection of cord blood is a standardized, straightforward process that takes place immediately after the baby is born and the umbilical cord is clamped and cut. This procedure is painless and carries no risk to either the mother or the infant. It is performed before the placenta is naturally delivered.
The healthcare provider inserts a needle into the umbilical vein, which is located in the section of the cord still attached to the placenta. The blood then flows by gravity into a sterile collection bag containing an anticoagulant to prevent clotting. Collection can be performed using two main techniques: in utero or ex utero.
In the in utero method, the blood is drawn while the placenta remains inside the mother, immediately following the birth of the baby. The ex utero method involves collecting the blood from the placenta after it has been delivered. Both methods yield comparable total nucleated cell counts, though the ex utero method often results in fewer quality issues like clotting.
Factors Influencing Collection Success
Several variables influence the final volume and the stem cell count of the collected cord blood unit. The timing of umbilical cord clamping is significant; delaying clamping, a practice recommended for infant health, substantially reduces the blood volume available for banking.
The expertise of the collector and the specific collection method used also play a role in the final yield. Collections performed by trained personnel tend to result in higher volumes and cell counts. The size and overall health of the placenta are relevant, as a larger placenta generally contains more residual cord blood.
Factors related to pregnancy and delivery, such as gestational age and maternal or fetal complications, can also impact the yield. These factors can influence the total nucleated cell count, sometimes leading to a unit that does not meet the minimum banking criteria.
Private Versus Public Banking Requirements
The intended destination for the cord blood, either a private or a public bank, directly impacts the acceptance criteria. Public banks collect cord blood donations for use by any patient who needs a transplant. Because these units must be capable of treating unrelated patients, including adults, public banks maintain stringent minimum requirements for cell counts and volume.
Public banks often reject units that do not meet these high thresholds, sometimes discarding up to 70% of collected units. They are required to follow strict quality assurance and regulatory standards, as the unit may be shipped internationally. The family relinquishes all ownership rights to the unit once it is accepted.
Private banks, in contrast, store the cord blood exclusively for the family’s potential use, making their acceptance criteria less restrictive. Since the unit is primarily intended for the child donor or a closely related family member, a smaller cell count may still be clinically useful. Private banks may store units that a public bank would reject, although storage of a low-cell-count unit does not guarantee its future utility.