Cord blood banking involves collecting and preserving blood from the umbilical cord and placenta for potential future medical use. This process secures hematopoietic stem cells, which can be used in transplants to treat various conditions. For parents considering banking, the key concern is not the physical volume collected, but the quantitative requirements for a successful, usable unit. The functional amount of a cord blood unit relies on specialized laboratory measurements that indicate its potential for a successful transplant.
The Critical Measurement: Total Nucleated Cell Count
The physical volume of the collected cord blood unit, measured in milliliters, is less important than the total number of cells it contains. The primary metric used is the Total Nucleated Cell (TNC) count, which represents the total number of white blood cells present. This measurement is considered the most reproducible and reliable initial indicator of a unit’s quality across banking systems.
Beyond the TNC count, an even more specific measure is the count of CD34+ cells, which are the actual blood-forming stem cells within the unit. These specialized cells possess a protein marker, CD34, on their surface, allowing for direct quantification of the most therapeutically relevant population. Both TNC and CD34+ cell counts are reported to parents and transplant physicians to assess the unit’s suitability for a procedure.
The utility of a cord blood unit for a transplant is directly related to the recipient’s body weight, meaning a larger person requires a higher cell dose. A common guideline for therapeutic use is a minimum dose of at least 25 million TNCs per kilogram of the recipient’s body weight. For instance, a single unit of cord blood considered suitable for a child transplant needs a TNC count greater than 500 million.
An adult recipient, due to their higher body mass, requires a much larger cell dose, often necessitating a TNC count greater than 1.25 billion cells. A specific guideline for a single-unit graft is a minimum of 25 million TNCs per kilogram and 150,000 CD34+ cells per kilogram of patient weight. Collections that fall below these thresholds may still be banked for potential use in future regenerative therapies or clinical trials, but they are insufficient for a standard stem cell transplant.
Factors Influencing Cord Blood Collection Volume
While cell counts are the definitive measure of quality, the initial volume of blood collected influences the final cellular yield. The physical amount of blood collected at the time of birth is subject to several biological and logistical variables. A greater volume of cord blood collected correlates with a higher TNC and CD34+ cell count, increasing the likelihood of a successful banking unit.
One significant biological factor is the weight of the newborn and the size of the placenta. Studies indicate that neonates with a higher birth weight are associated with a greater collected blood volume and a higher yield of TNCs and CD34+ cells. Similarly, a heavier placenta is linked to a greater volume of cord blood available for collection.
The timing of the umbilical cord clamping also plays a role in the final collection volume. Procedures that involve immediate clamping, as opposed to delayed clamping, often leave more residual blood in the umbilical cord and placenta for collection. Additionally, the method of delivery affects the collection, with cesarean sections yielding a greater blood volume and TNC count compared to vaginal deliveries.
The skill of the healthcare professional performing the collection is a determining factor in maximizing the volume. The collection must be performed quickly, typically within five to ten minutes of delivery, to prevent the blood from coagulating within the collection bag. Gestational age can also affect the collection, as an increase in age beyond a certain point correlates with a decrease in the collected blood volume and CD34+ cell count.
Processing and Quality Assessment of Stored Units
Once the cord blood unit arrives at the banking facility, it undergoes a series of laboratory steps to prepare it for long-term storage and confirm its viability. This processing is time-sensitive and is typically completed within 48 hours of collection to ensure maximum recovery of the stem cells. The first step involves evaluating the unit’s initial volume and TNC count to determine if it meets the bank’s minimum criteria for further processing.
The most important procedure is volume reduction, which concentrates the stem cells and removes unnecessary components like red blood cells and plasma. This is accomplished using automated systems, such as Sepax or AXP, which employ centrifugation to separate the blood into its constituent layers. Red blood cells are largely removed because they can be associated with adverse side effects if too many are infused during a transplant.
Volume reduction isolates the ‘buffy coat,’ which contains the concentrated white blood cells and stem cells, resulting in a final product volume of approximately 20 to 25 milliliters. This reduced volume allows for a more uniform freezing process, minimizing cell damage during cryopreservation. A cryoprotectant agent, commonly Dimethyl Sulfoxide (DMSO), is added to shield the cells from harm caused by freezing temperatures.
The final quality assessment includes infectious disease testing on a maternal blood sample to ensure the unit is safe for clinical use. After the unit is frozen in liquid nitrogen vapor, a final quality report is generated for the parents. This report confirms the unit’s final TNC and CD34+ cell counts, along with the post-processing cell viability, providing the definitive measure of the stored unit’s potential for therapeutic application.