Selecting donors of platelets for refractory patients on the basis of HLA antibody specificity

BACKGROUND: Patients who are refractory to platelet transfusion as a result of HLA alloimmunization are generally given HLA-matched or crossmatched pl atelets. However, HLA-matched platelets that are matched at HLA-A and -B lo ci (A-matched) or those without any mismatched or cross-reactive antigens ( BU-matched) are frequently unavailable. A disadvantage of crossmatching is that crossmatched platelets have a shelf life of only 5 days, so that cross match tests must be performed frequently for patients requiring long-term p latelet transfusions. An alternative method is the selection of platelets a ccording to the patient's HLA antibody specificity, called the antibody spe cificity prediction (ASP) method. STUDY DESIGN AND METHODS: An anti-human globulin-enhanced microlymphocytoto xicity test modified by a double addition of serum and a computer program w ere used to determine the specificity of patients' HLA antibodies. Platelet crossmatching was performed with a solid-phase adherence assay. The percen tage of platelet recovery (PPR) was determined in 1621 platelet transfusion s in an observational study in 114 patients, and the PPR of platelets selec ted by the ASP method was compared with the PPR of those that were HLA-matc hed, crossmatched, or randomly selected. The numbers of potential donors in files of HLA-typed donors as identified by HLA matching vs, the ASP method were determined. RESULTS: After adjustments for covariates, the mean +/- SEM PPR was similar for HLA-matched (21 +/- 4%), cross-matched (23 +/- 4%), and ASP-selected ( 24 +/- 3%) platelets and was significantly lower for randomly selected (15 +/- 1.4%) platelets. For 29 alloimmunized HLA-typed patients, the mean numb er of potential donors found in a file of 7247 HLA-typed donors was 6 who w ere an HLA-A match (median = 1), 33 who were an HLA-BU match (median = 20), and 1426 who were identified by the ASP method (median = 1365). CONCLUSION: The ASP method of donor selection for refractory alloimmunized patients appears as effective as HLA matching or crossmatching. Far more do nors are identified in a file of HLA-typed donors by the ASP method than by HLA matching, and this indicates that the ASP method provides important ad vantages regarding the availability of compatible platelet components.