Coagulation laboratory tests

Platelet antibodies

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PubMed Search: Platelet antibodies [title]

Jeremy C. Parsons, M.D.
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Table of Contents
Definition / general | Laboratory
Cite this page: Parsons JC. Platelet antibodies. website. Accessed November 29th, 2023.
Definition / general
  • Either autoimmune (idiopathic thrombocytopenic purpura), alloimmune (neonatal alloimmune thrombocytopenia, post-transfusion purpura, platelet transfusion refractoriness) or heparin-induced
  • These tests must be ordered and interpreted cautiously, considering the clinical presentation (Blood 1997;89:1112)

  • Platelet antibody disorders:
    • Drug-induced thrombocytopenia:
      • Detected by a difficult serotonin release assay (add patient plasma / serum plus drug and platelets with radiolabeled serotonin; drug antibodies, if present, stimulate platelets and radioactive serotonin is released)
      • Also detected with flow cytometry
      • Offending drugs include quinine and quidinine, sulfonamides, sulfonylureas, gold salts, salicylates
      • Mechanism is either non-immune (marrow suppression or non-immune destruction) or immune (platelet counts due to immune causes may drop to < 10K, return to normal within 7 days of stopping offending drug)
    • Idiopathic thrombocytopenic purpura (ITP):
      • Autoantibody against platelets, usually directed against GP IIb / IIIa, less commonly GP Ib / IX
      • Diagnosis of exclusion; usually resolves in children but is chronic in adults
      • Tests to order include peripheral blood smear, CBC, HIV, thyroid function tests, liver function tests and bone marrow biopsy
      • Although not technically contraindicated, platelet transfusions tend to be futile until the offending antibody is removed via some kind of immunosuppression
    • Neonatal alloimmune thrombocytopenia (NAIT):
      • Incidence of 1 per 1 - 5K live births
      • Father and newborn have antigen that mother lacks, mother produces antibodies to this antigen (usually PI - A1 component of GP IIb / IIIa), which crosses the placenta and destroys fetal platelets
      • Newborn platelet counts are < 100K at birth, return to normal within 2 weeks
      • Newborn can sometimes develop intracranial hemorrhage due to extremely low platelet count
      • If possible, give platelets negative for the antigen the mother lacks; otherwise, treatment of choice is washed maternal platelets
    • Platelet refractoriness:
      • In thrombocytopenic patients with multiple platelet transfusions, due to formation of HLA - A, HLA - B or less commonly ABO antibodies that destroy transfused platelets
      • Platelet crossmatch using immobilized platelets may be performed in referral centers
    • Post-transfusion purpura:
      • Patient has antibody directed against transfused platelet antigen absent on patients platelets
      • For unknown reasons, these antibodies also destroy platelets own antigens
      • Typically antigen is PI - A1 component of GP IIb / IIIa or an HLA antigen the patient lacks
      • Patients have sudden onset of severe thrombocytopenia 5 - 12 days after transfusion of platelet product, resolves 14 days after transfusion
      • In thrombocytopenic phase, common anti-platelet antibodies (GPIIb - IIIa, GPIb - IX and GPIa - IIa) are present, in addition to antibodies to the specific antigen the donor platelets express that precipitated the event
      • After resolution of the PTP episode, the general platelet antibodies will disappear, while the donor specific platelet antibodies will persist (Vox Sang 1999;76:120)
  • Types of tests:
    • ELISA: test for specific antiplatelet antibodies; antigen of interest is bound to surface of microtiter plate, then add patient plasma and antibody will bind to antigen
    • Antigen capture immunoassay: specific antigens are bound to solid phase, then add patient serum and patient antibodies will bind to antigens
    • Platelet antigen typing by antigen capture immunoassays: patients platelet antigens are immobilized by monoclonal antibodies onto a solid phase; then add antibodies of known specificity (Am J Clin Pathol 1990;93:552)
    • Flow cytometry: may be used
    • Lymphocytotoxicity assay: determine percent reactive antibody (HLA antibodies in patients who are refractory to platelet transfusions)
    • Polymerase chain reaction: can be used to identify patients platelet antigens
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