The risk of abbreviating the major crossmatch in urgent or massive transfusion.

The risk of abbreviating the major crossmatch in urgent situations by issuing blood after an "immediate spin" phase was evaluated by a retrospective study of 82,647 crossmatches performed on serum from approximately 13,950 patients. Although the initial screening test for unexpected antibodies for all patients failed to show agglutination or hemolysis of the reagent red blood cells, agglutination was subsequently noted during at least one crossmatch performed for 148 of them. Further evaluation of these patients' serums indicated that most positive reactions were due to weakly reactive low thermal amplitude antibodies. Eight of the incompatible crossmatches were related to antibodies in the Kell, Kidd or Rh systems, and a ninth antibody, anti-E, was identified through subsequent evaluation of a cold antibody-induced crossmatch incompatibility. Issuance of blood in urgent situations after an "immediate spin" phase of the crossmatch, for patients whose red blood cells have been typed, and whose serums have been screened for unexpected antibodies, has a low level of risk.