Donor selection for alloimmunized patients by platelet crossmatching of random‐donor platelet concentrates

Samples obtained from bag segments of stored platelet concentrates (PCs) were crossmatched with sera from alloimmunized patients to identify potentially compatible donors. Sera from 41 patients who were refractory to random‐donor platelet transfusions were tested. All sera had lymphocytotoxic antibody (LCTAb), and 37 patients had LCTAb that reacted strongly against >75 percent of the cells in the panel. At least 18 units of PCs were tested per patient. Sera from 33 patients were tested by microenzyme‐linked immunosorbent assay (microELISA). Crossmatches with 703 (74 percent) of 944 PCs were positive, 23 percent were negative, 3 percent were indeterminate. Eight additional patients were also tested with a solid‐phase system; 352 (85 percent) of 417 crossmatches were positive and 15 percent were negative. Patients with more reactive LCTAb had very few (often 0–2) in vitro compatible units. Thirty‐four transfusions of pooled compatible PCs, all stored <3 days, were administered to clinically evaluable patients. Six of 20 transfusions selected by microELISA produced satisfactory increases (corrected count increments [CCIs] >7500) 10 minutes after transfusion in 4 of 14 patients. Eight of 14 transfusions selected by solid‐phase produced CCIs >7500 in 5 of 8 patients. Although it is difficult to select large numbers of compatible units for heavily alloimmunized patients by these techniques, some transfusions were successful in patients who had very few HLA‐compatible donors. This approach may be of particular value in emergency situations.