(P-TS-118) Swiss Haemovigilance Data Indicate Adverse Events Due to Incorrect Use of O RHD1 Negative Red Blood Concentrates and Support Benefit of Extended Monitoring

Background/Case Studies: The proportion of the Rhesus negative blood group in the Swiss population amounts to 15% of which 6% are of group O Rhesus D negative (RH1-). Disproportionate demand of O RH1- Red Blood Concentrates (RBC) by hospitals and depots led to specific national recommendations on clinical use of O RH1- RBC at the end of 2024. Data on use of RH1- RBC in Switzerland is limited, correct application can only be evaluated indirectly.

Study

Design/Methods: Obtention of base line data on O RH1- RBC use in 2023 and 2024 prior to implementation of the recommendation using a) data on proportion of issued RH1- units to hospitals and on shortage periods. b) mandatory reporting data on RH1+ RBC transfusions to RH1- patients to Swissmedic (SMC).c) mandatory reporting of post-transfusion alloimmunization to SMC (Swiss guidelines prioritize RH1 identical RBC transfusions).

Results/Findings: The proportion of issued O RH1- RBC showed regional heterogenicity and disproportional distribution to occurrence in the general population, with figures varying between 9% and 16%. Shortage of O RH1- RBC has occurred in Switzerland for around one-fifth to one-quarter of the year in 2023 and 2024. Transfusion of O RH1+ RBC to O RH1- patients has been reported in 44 (2023) and 51 (2024) cases. Table 1 shows data on number of units transfused before RH1 switch with increasing switches occurring before the recommended minimum (4 units) in 2024 compared to 2023. In both years 196 RH1 alloimmunizations (13,6%) of a total number of 1444 RH antigen alloimmunizations were reported.

Conclusions: Data suggest unnecessary excessive ordering or consumption of O RH1- RBC and inconsistent implementation of guidelines regarding RH1 identical transfusions in Switzerland. Available data, however, is limited to the monitoring of consumption and adverse events and is affected by under-reporting within the passive haemovigilance reporting system. Thus, they provide limited insights into clinical context and adherence to guidelines. Hospital-statistics on blood group O and RH1- status of RBCs and patients could be beneficial in gaining better understanding and is recommended in the recently issued recommendation on use of group O RH1- RBC. Continued and extended monitoring will allow comparison with baseline data, evaluation of availability of RBC O RH1- and can help to assure its continuous correct use to avoid adverse consequences for patients.