(P-BB-20) Can We Consider Platelets in Platelet Additive Solution as “High Titre Negative” for Anti-A/B?

Background/Case Studies: Currently, most clinical guidelines recommend transfusing ABO-identical platelets when possible. In England apheresis or pooled (from 4 donors) platelets are labelled as ‘high-titre (HT) negative’ if all donations used in the component have tested negative at 1:128 for IgM anti-A/B, thus reducing the risk of haemolysis if transfusing ABO minor-incompatible platelets.
Pooling of platelets and suspension in 65% platelet additive solution (PAS) reduces individual donation anti-A/B levels in the platelets. It has been questioned whether this reduction is sufficient to consider platelets in PAS as low-titre for anti-A/B even if donors are not selected as ‘HT negative’.
Data are presented on anti-A/B titres of English blood donors, and modelling of the likelihood of apheresis or pooled platelets in PAS being at/above various levels of anti-A/B including the HT threshold 1:128 IgM.

Study

Design/Methods: The following data was used to simulate (in R) the creation of 10,000 group O platelet pools.
1. The distribution of IgM and IgG anti-A and anti-B antibody levels using ID-card methodology from 451 donors with known ABO group, sex, and HT screening results.
2. The observed HT positivity rates among whole blood donations, by ABO group, sex, and ethnicity from ~3 million whole blood donations.
3. The typical male: female split of donations used to make platelet pools.
The proportion of the simulated pools having antibody levels at/above various thresholds was then calculated for group O and A platelets.

Results/Findings: Single donor apheresis platelets had higher levels of residual antibodies than pooled platelets (Table 1).

Conclusions: The likelihood of final platelet components being at/above our definition of HT positive, if donor HT status is unknown, is reduced by pooling and storage in 65% PAS.
• For group O platelets this risk appears significant, compared to testing and ensuring that the final product is low titre.
• For group A platelets this risk is low, but larger data sets are required to determine the frequency of very high antibody levels in the donor population to help assess if the risk is clinically acceptable.

Importance of research: Hospitals frequently request high titre (HT) negative platelets for transfusion across ABO group when ABO-compatible platelets are unavailable creating pressure on the HT negative platelet supply and wastage of HT positive platelets. Understanding the clinical risk when diluting platelet pools in different percentages of PAS (which could lead to more HT negative pools being available) is important when addressing these platelet supply issues.