Platelet transfusion therapy. One-hour posttransfusion increments are valuable in predicting the need for HLA-matched preparations.

Seventy-nine platelet transfusions to 73 thrombocytopenic patients with cancer were analyzed to determine whether a platelet count obtained one hour after transfusion could help differentiate between alloimmunization and other clinical factors that result in rapid platelet destruction. These transfusions were selected because 18- to 24-hour increments were inadequate in response to fresh, random donor platelets. A corrected count increment (Cl) (Cl=[posttransfusion count-pretransfusion count]Xbody surface area [sq m]/platelets transfusedX10'') at one hour of 10X103/microliter or greater was associated with absence of lymphocytotoxic antibody, whereas increments of less than 10X103/microliter were generally associated with high levels of strongly cytotoxic antibody. HLA-matched transfusions produced no improvement in increments when the previous one-hour Cl had been 10X103/microliter or greater, whereas in the other group significantly better increments were obtained. A one-hour posttransfusion count is a simple test that correlates well with the presence of antibody against HLA antigens, is valuable in predicting the need for HLA-matched platelets, and helps avoid wasteful, empirical use of such transfusions.