Immunological Considerations Attending Platelet Transfusion

Iso‐immunization against platelets occurs infrequently with less than ten transfusions, but the frequency rises steadily with the number of transfusions until all patients eventually become immunized. Characteristics of specific antigens and antibodies that have been identified to date are described briefly and the relative merits of various immunologic technics used to measure platelet iso‐antibodies are discussed. More than half of the anti‐platelet iso‐anti‐bodies that arise after transfusion are “incomplete” and cannot be detected by conventional serologic tests. Some of these antibodies have been identified by “blocking” tests or by passive transfer. These findings explain why refractoriness to platelet transfusions is not always accompanied by serologic evidence of immunization. Isoimmune destruction of platelets is a relatively innocuous occurrence and does not contra‐indicate further trials of platelet transfusion. Although platelets can be matched under some circumstances when iso‐immunization has taken place, at present empirical selection of donors based on survival of transfused platelets appears to be the best approach to platelet transfusion in sensitized individuals.