A predictive approach achieved “an unprecedented” 100 percent single-session success rate in male donors and 94.9 percent overall, according to the study
Jeddah, Saudi Arabia, 7th June 2026
A new algorithm-guided protocol has helped transplant teams complete stem cell collection in a single session for nearly all donors, addressing one of the most persistent challenges in allogeneic stem cell transplantation: predicting how many cells a healthy donor is likely to yield before collection begins.
Physicians at King Faisal Specialist Hospital and Research Centre in Jeddah, Saudi Arabia, developed and applied the protocol to 138 consecutive allogeneic stem cell donors. According to the study, the protocol achieved “an unprecedented 100 percent single-session success in male donors and 94.9 percent overall,” while eliminating the need for third and fourth collection sessions altogether.
The findings were published in Blood Global Hematology, a journal of the American Society of Hematology. In the paper, the authors wrote that the results challenge the field’s acceptance of repeat apheresis as inevitable and support algorithm-guided single-session collection as an achievable standard in allogeneic transplantation.
Stem cell collection is a critical step before transplantation. In allogeneic transplantation, healthy donors receive a mobilizing medication that moves stem cells from the bone marrow into the bloodstream. The cells are then collected through apheresis, a process in which blood is drawn from the donor, passed through a cell separator, and returned to the body.
But donor response varies widely. Some donors mobilize enough cells for a patient in one session, while others fall short and must return for additional collections. In some medical centers, single-session failure rates have been reported to reach 60 percent or higher.
For healthy donors, repeated sessions can mean more time on mobilizing medication, more hours connected to the collection machine, and greater procedure-related burden. For patients waiting for transplantation, delays in collection can slow the path to treatment.
Large registry data cited by the researchers underscore why repeat collection is more than an inconvenience. Figures from the U.S. National Marrow Donor Program show that two-day collections were associated with a higher likelihood of hospitalization for serious adverse events, 6 percent compared with 1 percent in single-day collections, a sixfold difference. The data reinforce the need for collection strategies that reduce unnecessary repeat procedures for healthy volunteer donors.
The new protocol was designed to address both problems: the uncertainty before collection and the added donor risk that comes with repeat procedures. Using an algorithm, it estimates the expected CD34+ stem cell yield before collection begins, allowing the medical team to plan the first session around each donor-recipient pair while staying within defined safety limits for processed blood volume and apheresis duration.
The gains were achieved without exceeding the study’s safety boundaries. The authors reported that collection success came from algorithmic precision rather than procedural excess, with procedures kept within a 15-liter processed blood volume ceiling and a five-hour duration limit.
“Sparing healthy donors from repeated stem cell collection sessions is both a clinical and an ethical priority,” said Professor Ashraf Dada, Chair of the Department of Pathology and Laboratory Medicine at King Faisal Specialist Hospital and Research Centre in Jeddah and the study’s principal investigator.
Dada said the algorithm was developed over three years and tested on 138 donors. It enabled the team to plan the first session with nearly 92 percent predictive accuracy in estimating the number of cells to be collected.
“This improves the donor’s experience and safety, supports advance planning, and accelerates treatment for patients awaiting transplantation,” he said.
The study also documented encouraging patient outcomes, with survival reaching 91.2 percent at 100 days after transplantation, alongside successful early engraftment. The findings suggest that collection efficiency for healthy donors can be improved while maintaining strong early outcomes for recipients.
For transplant programs, the work points to a shift in how stem cell collection may be planned. Rather than treating repeat apheresis as an unavoidable consequence of donor variability, the study suggests that predictive planning can help reduce unnecessary repeat procedures, protect healthy donors, and help patients reach treatment sooner.
