According to the Swiss recommendations, in absence of clinically significant antibodies (AB) red blood cell concentrates (RBC) can be released by type and screen. The implementation of these recommendations in daily practice have shown that only 15% of the pre-transfusion tests require an additional crossmatch. But although recommendations set several safety criteria for their application, a residual risk of hemolytic transfusion reaction persists.

We investigated retrospectively the hemolytic transfusion reactions (HTR) reported to the Swiss mandatory hemovigilance system between 2008 and 2023. We considered the specificity and the clinical significance of the AB, and the kind of HTR (severity, acute or delayed). We excluded hemolysis related to auto-AB, HTR caused by other products then RBC, and delayed HTR (AB not identifiable by serological crossmatch). We evaluated in which cases performing a crossmatch would have prevented from HTR and calculated the residual risk based on the number of RBC issued in the same time interval in Switzerland.

Between 2008 and 2023, 158 HTR were reported. Of these, 35 were associated with auto-AB or related to other products. In 115 of the 123 remaining HTR, the AB specificity was detected by the AB screen. Of the remaining 8, 7 caused a delayed HTR and/or were not clinically significant (3 Bg(a), 1 P1, 1 Yt(b), 1 Co(b), 1 Ch/Rg). Only one acute HTR with mild hemolysis caused by an anti-Wr(a) AB would be prevented by additional crossmatch. Thus, according to these data the evaluated risk would be 1 : 4"097"234 issued EK in 15 years. Considering additionally 1 anti-Co(b) and 1 anti-Yt(b) AB, each involved in a delayed HTR, as potential cause of an acute HTR in a different setting, the risk of a mild HTR would be about 1 : 1"365"745.

According to the hemovigilance data over the past 16 years, the residual HTR risk in Switzerland seems to be very low. Even though the reporting of transfusion-related allo-AB and of HTR is mandatory, we are aware that underreporting probably occurs. On the other side, post-transfusion tests regularly performed after HTR include the serologic crossmatch, and AB not identified in the AB screen are included in the reports. Even if low, the acceptance of the residual risk should be evaluated by all involved stakeholders.

No conflict of interest related to the abstract.