Identification and Management of the Backup Donor: Recommendations from the WMDA

Timing of allogeneic hematopoietic cell transplantation (HCT) is a crucial factor that can significantly impact transplant outcome with delay potentially leading to disease progression or patient condition deterioration. While availability of unrelated donors is a key performance indicator of the World Marrow Donor Association (WMDA), registries often struggle to meet benchmark thresholds established to ensure that patients have timely access to transplant. At workup (WU), if the donor is unable to proceed due to unanticipated personal or medical reasons, the impact to patient care can be catastrophic; the transplant centre (TC) must urgently identify another suitable candidate for donation whose requisite testing and preparation can significantly extend the timeline to transplant. In 2024, global organisations indicated that 16% of all WU were canceled due to donor-related reasons, although unavailability rates varied substantially between participating registries. Despite initial rebound post-pandemic, donor unavailability at WU has increased steadily since 2021, now exceeding that experienced at the height of the pandemic in 2020 where it peaked at 15.2%.2 These findings underscore the need for patient registries and TC to define backup donor (BUD) strategies to mitigate patient risk. However, differences in national practices have resulted in variability in the search strategies, policies, and procedures currently used by organisations to ensure that various donor and treatment options are available for patients to minimise the risk of delayed transplant if a primary donor becomes unavailable. Reciprocally, these inconsistencies, combined with insufficient TC communication, can cause confusion for donor registries and donor centers (DC), potentially resulting in misinformed donors, unnecessary WU and/or product collection, and increased resource burden. The WMDA believes it is imperative that both donor and patient registries define policies for the proactive identification and management of BUD to minimise patient risk and to increase transparency and safety for BUD. Management of BUD at WU is a complex issue in which patient access to timely transplant must be balanced with the impact on prospective donors, DC and collection centre (CC) resources, and potential costs incurred by TC and their respective registries. Lack of standardisation in practice, including the definition of a BUD, has prompted the WMDA to provide the following guidance toward BUD policy and introduce a common language for describing BUD activities and emerging practices in donor management. We encourage organisations to define their policy in observation of the recommendations set forward herein.