The importance of ABH antigens in platelet crossmatching.

In the present study, the frequency with which ABH incompatibility could be detected in platelet crossmatches was determined. The effect of chloroquine elution on ABH antigens was also evaluated, and a technique was developed to remove IgG anti-A from group O plasma using a chemically synthesized human blood group A trisaccharide antigen covalently linked to crystalline silica (Synsorb-A). Group O plasmas were found to be incompatible with 52 percent of group A platelets and 17 percent of group B platelets (p less than 0.05). In contrast, anti-A from group B plasmas rarely produced a positive crossmatch, and no anti-B that reacted with platelets could be demonstrated in group A plasmas. IgG anti-A reactions with group A platelets were eliminated in 100 percent of the group O plasmas tested after treatment with the synthetic solid-phase immunoadsorption technique. Synsorb-A may be a useful adjunct to platelet serologic testing when group O sera need to be tested against A platelets. Group A platelets bound less anti-A after exposure to chloroquine, but only 17 percent of platelets became negative when crossmatched with group O plasma. It was concluded that increased IgG binding occurs in a majority of platelet crossmatches using a k-ELISA technique when group O recipients are tested against group A donors. These results offer a potential explanation for conflicting results in studies of transfusion results with ABH-incompatible platelets. Transfusions of group B platelets to incompatible recipients may be more likely to yield satisfactory increments than incompatible transfusions of group A platelets, but this remains to be proven. There appear to be significant differences between red cells and platelets in regard to serologic reactivity in the ABH system.