Aims: To ascertain the effects of allowable sampling time prior to red cell transfusion when screening for alloantibodies, we compared antibody detection rates and frequencies of delayed hemolytic transfusion reactions (DHTRs) among patients drawn within two weeks versus patients drawn within one week of transfusion.

Methods: Alloantibody screening for 32,601 patients from January 1997 through August 2006 was done within two weeks of transfusion, and for 44,896 patients from September 2006 through March 2017 was done within one week. Among transfusion recipients, 6,234 screened within two weeks and 8,066 screened within one week were evaluated for DHTR.

Results: Alloantibodies were detected in 1.2% of cases screened within two weeks and in 1.3% of cases screened within one week, with no statistical difference. Anti-Fyb was more frequently detected (115.8 versus 39.9 per 100,000 patients) among those screened within one week (p <0.001); anti-Dia showed a similar trend, but without statistical significance (p =0.065), whereas anti-c was less frequently detected (p <0.05). The number of DHTRs observed was significantly lower among those screened within one week, with two cases (1 in 4,031) versus eight (1 in 779) among those screened within 2 weeks (p <0.05).

Conclusion: By shortening allowable sampling period for red cell alloantibody screening from within two weeks to within one week of transfusion, the detection rate of clinically significant antibodies, except for anti-c, increased, and the frequency of DHTR recipients decreased.

Keywords: Alloantibody, Clinically significant antibody, Delayed hemolytic transfusion reaction, Irregular antibody screening