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Platelet antibodies may be allo- or autoantibodies and may be directed to a wide range of antigenic "targets" carried on platelet cytoplasmic membranes.
Platelet alloantibodies are involved in several clinical situations such as alloimmune platelet refractoriness (APR), neonatal alloimmune thrombocytopenic purpura (NATP), and posttransfusion purpura (PTP). In these settings, the antibodies, usually HLA Class I in the case of APR, and platelet-specific antibodies eg, HPA-1a (PLA1) in the case of NATP or PTP, are found in the patient's plasma and are detected by tests performed on serum.
In contrast, conditions such as idiopathic thrombocytopenic purpura (ITP), systemic lupus erythematosus (SLE), or sepsis are associated with the presence of excessive platelet associated immunoglobulin usually IgG. Testing for cell bound platelet antibody is indicated for the diagnosis of these autoimmune conditions. In some cases of ITP, platelet antibodies can also be found in the patient's serum but with less frequently than cell bound antibody.
Evaluating cases of immune platelet refractoriness, post-transfusion purpura, or neonatal alloimmune thrombocytopenic purpura
Presence of reactivity to some glycoproteins has no clearly established clinical significance.
Results are based on clinical situation as well as test results.
Serum platelet antibody testing by solid-phase enzyme-linked immunoassay offers more than a positive/negative result. When the patient's serum is positive, the specific platelet glycoprotein will be identified as well as the probable specificity. The platelet glycoproteins reported are: IIb/IIIa, Ia/IIa, GPIb/IX. Specificities include the following: HPA-1a (PL[a1]), HPA-1b (PL[a2]), HPA-3a (BAK[a]/LEK[a]), HPA-3b (BAK[b]), HPA-5b (Br[a]), HPA-5a (Br[b]). Those specificities listed in parenthesis refer to old nomenclature. In addition, this assay screens for HLA Class I antibodies, but specificity is not determined.
No significant cautionary statements
An interpretive report will be provided.
1. Kiefel V, Santoso S, Weisheit M, et al: Monoclonal antibody-specific immobilization of platelet antigens (MAIPA): A new tool for the identification of platelet-reactive antibodies. Blood 1987;70:1722-1726
2. Moore SB, DeGoey SR: Serum platelet antibody testing: evaluation of solid-phase enzyme immunoassay and comparison with indirect immunofluorescence. Am J Clin Pathol 1998;109:190-195