Delayed Platelet Recovery After Allogeneic Peripheral Blood, Marrow and Umbilical Cord Stem Cell Transplantation: Risk Factors and Clinical Outcomes.

Several reports have shown that despite prompt neutrophil engraftment after allogeneic stem cell transplantation, there can be delayed platelet recovery, especially in umbilical cord blood (UCB) stem cell transplant recipients. This dichotomy in platelets and neutrophils engraftment is poorly explained. In addition, the risk factors and complications associated with delayed platelet recovery are not clearly identified.

We conducted a retrospective analysis to characterize the frequency of delayed platelet recovery and its associated risk factors and related complications. All allografts at the University of Minnesota between 2000 and 2005 were included.

875 patients with hematologic malignancies or benign disorders were included. Myeloablative conditioning was used in 576 (66%) patients and non-myeloablative conditioning in 299 (34%) patients. 343 (39%) patients received related donor and 532 (61%) unrelated grafts. The source of the graft was bone marrow in 226 (26%) patients, peripheral blood in 255 (29%) patients and UCB in 394 (45%) patients. 150 (17%) patients were excluded due to early death (n=87, 10%), graft failure (n=62, 7%) and second transplant without engraftment (n=1). The 60 day cumulative incidence of platelet recovery by donor type was UCB single cord 39% (n=180, CI 31-47%), UCB double cord 40% (n=206, CI 32-48%), URD mismatched 57% (n=28, CI 39-75%), URD matched 56% (n=117, 48-64%) and sibling 74% (n=319, 65-85%). Overall, 232 (32%) had delayed platelet recovery (platelets<50K by day 60) and 475 (67%) had successful recovery (platelets>50K by day 60). Cox regression analysis showed that variables significantly associated with delayed platelet recovery were donor type (UCB RR 0.3 [CI 0.2-0.35], p<0.01 vs sibling RR 1.0), ABO match (major mismatch RR 0.8 [CI 0.6-1.0], p<0.01 vs matched RR 1.0), CMV status (positive RR 0.8 [CI 0.6-1.0], p=0.04 vs negative RR 1.0) and the vs negative RR 1.0). Transplant related mortality (TRM) at 12 months was also higher in patients with delayed platelet recovery compared to patients with successful platelet recovery (30% vs 11%) (p<0.01). Risk factors for TRM by proportional hazard regression were delayed platelet engraftment (RR 3.9 [2.6-6.0], p=<0.01 vs early RR 1.0), HLA mismatched unrelated donor (RR 3.7 [CI 2.5-7.1], p=0.01 vs sibling RR 1.0), severe aGVHD (RR 1.8 [CI 1.2-2.8], p=0.02 vs no severe RR 1.0) and age > 35 (RR 1.6 [CI 1.0-2.5], p=0.03 vs age < 35 RR 1.0). Successful platelet recovery was associated with a 77% 1 year survival versus only 59% in patients with delayed platelet recovery (p<0.01).

These results suggest that delayed platelet recovery and poor graft function are common complications of allogeneic stem cell transplantation, especially after UCB grafts. Further study is needed to determine if modification of these associated risk factors will reduce the risks of severe complications and improve survival.

No relevant conflicts of interest to declare.