1. Single-Donor Platelets: Arguments for Preferential Use Paul M. Ness, MD Transfusion Medicine Division Johns Hopkins Medical Institutions

2. TRANSFUSION PRACTICES Platelets Prepared as a byproduct of whole blood collections or by apheresis Major use for (1) acute hemorrhage due to thrombocytopenia or (2)prophylaxis during periods of bone marrow aplasia Effectiveness limited by alloimmunization during chronic therapy or septic reactions until recently

3. APHERESIS PLATELETS POTENTIAL ADVANTAGES Reduction in infectious complications Reduction in transfusion reactions Ease of leukodepletion Reduction in transfusion frequency Treatment of alloimmunized recipients Prevention of alloimmunization

4. SPTR JOHNS HOPKINS (1987-1990) Incidence of 1:4200 transfusions in oncology patients Septic reactions were more common with random donor platelet concentrates (RDP) Reactions were more common with longer periods of storage Source was skin contaminant in 4/7 cases; bacteremic donor in 3/7 cases

5. Conclusions Single donor platelets substantially reduce but do not eliminate SPTR. Pretransfusion screening has substantially reduced SPTR, but pathogen redcution will be required to eliminate all SPTR. Although current risks of viral infections are miniscule, SDP may be of value to prevent emerging infections

6. Platelet Transfusion Reactions Febrile reactions due to white cells or cytokines produced during storage Allergic reactions TRALI

8. Moderate to Severe Reactions TRAP Study Temperature increase > 2 degrees C Chills with rigors Extensive urticarial eruptions Dyspnea Cyanosis Bronchospasm Anaphylaxis

11. Reduction in Transfusion Reactions Premedication is often prescribed but convincing data of efficacy are lacking Washing platelets reduces allergic reactions but increments and survival are compromised Limiting donor exposure should reduce reactions from contaminating elements ULR reduces febrile reactions

12. Ease of Leukodepletion Ongoing debate in the US about universal versus selective leukoreduction Current apheresis equipment produces SDP which routinely meet ULR requirements Filtration of PC to meet leukoreduction requirements is cumbersome

13. PLATELET TRANSFUSIONS Norol et al, BLOOD 1998 Higher platelet dosages increase the transfusion interval from 2 to 4 days Higher doses facilitate outpatient therapy. Importance of dose is controversial for prevention of bleeding in patients with hematologic malignancies; dose trial to be initiated by TMH Network

14. PLATELET ALLOIMMUNIZATION Most important long term complication of platelet transfusion therapy Incidence depends upon patients under study, previous transfusions or pregnancies, and intensity of therapy About 1/3 of patients with AML become alloimmunized and refractory to random platelets

15. PLATELET ALLOIMMUNIZATION About 50% of HLA “matched” transfusions are failures Alloimmunized recipients remain at risk for hemorrhage when transfusions fail Therapy for refractory patients is expensive

16. SELECTION OF COMPATIBLE DONORS Define antibody specificity and avoid incompatible antigens HLA matching ( family or volunteer) Platelet crossmatching Obtain compatible platelets by apheresis

17. ALLOIMMUNIZATION Therapy Prevention HLA matching Platelet crossmatching Experimental therapies Leukodepletion UV irradiation Reducing donor exposure with SDP is not effective

18. APHERESIS PLATELETS POTENTIAL ADVANTAGES Reduction in infectious complications Reduction in transfusion reactions Ease of leukodepletion Reduction in transfusion frequency Treatment of alloimmunized recipients Prevention of alloimmunization (UNPROVEN) Platelet quality

23. Summary We switched to SDP primarily because of the problem with SPTR; even with bacterial detection, we still believe that patient care is enhanced by using SDP. Avoiding pooling was a large motivation for the laboratory to move to SDP; with pool and store at the blood center now permissible, we might re- evaluate our position, depending upon the cost.