group-compatible plasma, rather than group-compatible platelets. Neither major nor
minor crossmatch is necessary prior to platelet transfusion unless the platelet product
contains many RBCs.
(3) Rh antigens are not found on platelets; however, patients may become
sensitized to Rh antigens from the RBCs contaminating the platelet concentrate. The
risk of forming anti-RhO has been shown to be approximately 8 percent, after 80 to 110
units of platelets. Because of the life-threatening nature of most cases of
thrombocytopenia, platelets from Rh-positive donors can be administered to
Rh-negative recipients; however, Rh-negative women in the childbearing age with a
nonmalignant disease should not receive platelet concentrates from Rh-positive donors
because of-the effect of possible anti-Rh on future pregnancy. Circulation of platelets
from Rh-positive donors in recipients with preformed anti-RhO is normal; thus, the only
concern is possible reaction to contaminating Rh-positive RBCs. If the platelet
concentrates are properly prepared, RBC contamination is 0.4 ml or less and, thus, a
red cell hemolytic reaction would not be expected even in a recipient with a preformed
anti-RhO antibody.
d. Platelet Compatibility. In addition to ABO antigens, platelets contain the
HLA antigens found on most tissues of the body and additional antigens that are unique
to platelets. Some patients may develop antibodies to these HLA or platelet antigens
following transfusion, pregnancy, or organ transplantation. When this occurs,
transfused platelets have a decreased recovery and a shortened intravascular survival.
These transfused platelets are ineffective in controlling hemorrhage. Compatible
platelets may be obtained by HLA-matching of patient and donor. The most likely
source of HLA identical or compatible donors would be the patient's family; however,
large files of HLA-typed donors are being developed for clinical research purposes.
HLA-matching of patients with unrelated donors may become practical. HLA-matching
using the lymphocytotoxicity assay may not be the best method of determining platelet
compatibility; however, it is the only one currently available on even a limited scale.
Thus, in patients who are unresponsive to the transfusion of platelets collected from
random donors, selection of donors based on HLA-typing may provide platelets with
better posttransfusion recoveries and survival.
e. Administration of Platelets.
(1) Patients with platelet or HLA antibodies may have febrile nonhemolytlc
reactions to Incompatible platelets. These reactions may be caused by incompatible
platelets or by Ieukocytes that invariably contaminate the platelet preparation. In
addition, platelets may be trapped in the pulmonary capillaries, causing dyspnea and
pulmonary edema. This is particularly likely if aggregates of platelets are infused. If the
platelets are properly prepared, they will contain very few aggregates.
MD0846
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