Isohemagglutinin titres: A comparison of pathogen reduced pooled platelets manufactured with platelet additive solution versus untreated pooled platelets

Introduction

Limitations in platelet inventory necessitate the use of ABO-incompatible (ABOi) platelets for transfusion with possible risk of an acute hemolytic transfusion reaction due to the presence of high titre (HT) isohemagglutinins (ISO). Pooled platelets psoralen-treated (PPPT) are manufactured following the division of 7 donor buffy coats in a platelet additive solution (PAS). The PAS:plasma ratio of 60:40 provides a dilutional effect on ISO levels. The purpose of this study is to compare the proportion of PPPT that test ISO HT positive versus untreated 4 donor platelet pools without PAS (UPP).

Methods

Component-based ISO titration was performed on 1001 UPP (November 8 2022-February 8 2023) and 1019 PPPT (June 1 2023-August 31 2023) followed by testing of 834 additional group O PPPT (September 1 2023-January 19 2024) to refine the HT rate estimate. All testing was performed at a single laboratory by a manual immediate spin tube method using an aliquot of platelet supernatant diluted 1:50 with saline tested separately against A1 and B cells. Agglutination with either/both A1 and B cell(s) constituted a positive HT result. The proportion of components with HT results were compared for PPPT vs UPP. Statistical analysis was performed using SAS with P-values calculated using the chi-square method.

Results

Of 1019 PPPT in PAS, 3 (0.29%) tested HT positive and all were group O. By comparison, 64/1001 (6.4%) UPP were HT positive (P-value <.0001). The rate of HT positivity by ABO blood group for PPPT vs UPP: Group O 3/559 (0.54%) vs 53/496 (10.6%) (P-value <.0001); Group A 0/439 (0%) vs 9/468 (1.9%); Group B 0/21 (0%) vs 2/37 (5.4%). For group A and B platelets, the relatively low rate of HT positive events in both UPP and PPPT precluded meaningful statistical comparison. Testing of 834 additional group O PPPT yielded 6 HT positive components for a total of 9/1393 (0.65%) HT positive group O PPPT (99% CI 0.23-1.43%).

Conclusions

Greater than 99% of pathogen reduced pooled platelets in PAS have low isohemagglutinin titres using a common component-based testing assay. For PPPT, none of the group A or B tested HT positive with 0.65% positivity in group O. The significant reduction in HT positive pooled platelet components with this new manufacturing method confers a greater safety profile when ABO incompatible platelet transfusion cannot be avoided. These findings may impact hospital decisions around inventory management, platelet selection and titre testing.