Alloimmunisation of Patients Undergoing Bone Marrow Transplantation in the Setting of Leucodepleted Apheresis-Collected Single Donor Platelets.

Introduction: Immune platelet transfusion refractoriness often leads to requirements for specialised platelet products. Our patients are screened weekly for the presence of platelet antibodies during bone marrow transplantation (BMT) protocols and are routinely issued leucodepleted (LD) packed red cells and apheresis-collected leucodepleted single donor platelets (LDSDP).

Aims: We assessed the alloimmunisation rate in BMT patients, the impact of this on transfusion requirements and addressed the value of continued routine platelet antibody (PAI) screening in the setting of LDSDP.

Results: Routine PAI screens performed on 148 BMT patients over 33-months (January 2002–September 2004) were reviewed; 71 autologous, 55 sibling allogeneic and 22 matched unrelated donor (MUD) BMT patients. Thirteen patients were alloimmunised (antibody specificity anti-HLA (11 patients) and anti-HPA/platelet glycoprotein (2 patients)). The overall alloimmunisation rates were 8.8% (sibling allogeneic 14.5%, MUD 9.1% and autologous 4.2%). Alloimmunisation rates for women were 4.15 times higher than for male patients. Risk factors for secondary alloimmunisation were present in 92.3%. Seven of 9 alloimmunised women had children, 1 of 2 nulliparous women and all 4 male patients had extensive transfusion histories (all 5 were also transfused at other centres where LDSDP were not standard). Alloimmunisation was detected earlier in females, usually on first PAI screen and before transfusion. Alloimmunised patients required specialised platelet products (crossmatched, HLA, directed donations or frozen-thawed SDP). These measures resulted in improved post platelet transfusion increments.

Conclusions: Alloimmunisation continues to occur despite use of leucodepleted transfusion products. Evidence supporting secondary alloimmunisation was present in the great majority of patients with more female patients alloimmunised largely due to their parity. Secondary alloimmunisation is not prevented by transfusion of leucodepleted blood products, however early detection of alloimmunisation assists transfusion decisions. There is indication from this data that platelet antibody could be limited to a PAI screen at presentation (together with HLA typing) in patients who have been transfused or pregnant with a repeat PAI performed following transfusion. Further testing could be delayed until platelet transfusion refractoriness is suspected.