Equis ISSN 2398-2977

Blood: thrombocytopenia

Contributor(s): Cody Coyne, Mark Holmes, Prof Derek Knottenbelt, Ruth Morgan, Vetstream Ltd


  • Rare.
  • Cause: idiopathic; secondary to drug administration, neoplasia (lymphosarcoma    ) or infection.
  • Signs: petechial/ecchymotic hemorrhages, epistaxis, hematuria, melena. Signs associated with the primary disease.
  • Diagnosis: hematology analysis (severe thrombocytopenia   Blood: platelet evaluation  ), delayed bleeding time.
  • Treatment: corticosteroids   Dexamethasone  (unless active viral infection), azathioprine, platelet rich plasma administration, available at some referral institutions.
  • Prognosis: depends on underlying cause.



  • Platelets participate in blood coagulation mechanisms and maintain the integrity of vascular endothelial structures. They are an essential component of primary hematuria.
  • Primary immune-mediated thrombocytopenia involves the evolution of a close of B-lymphocytes that begin to produce immunoglobulin against various glycoprotein complexes expressed on the exterior surface membrane of platelet populations.
  • Binding of immunoglobulin to the surface membrane of platelets promotes, cytolysis, agglutination, complement activation and accelerated removal of platelets from the systemic circulation by the mononuclear phagocytic system residing primarily within the spleen and liver. More antibody = further destruction and removal    →   faster onset of signs.
  • Antibodies also affect megakaryocytes in bone marrow   →   reduced platelet production.
  • In primary IMT, the binding avidity of immunoglobulin is directed specifically against certain cell membrane associated antigens, but in secondary IMT, immune complexes non-specifically bind to the exterior surface of platelets.
  • Secondary immune-mediated thrombocytopenia has been found to be induced by a wide spectrum of pharmaceutical agents, several infectious pathogens and neoplasia.
  • In most cases the etiological cause cannot be determined (suspected primary thrombocytopenia).
  • Drugs associated with secondary thrombocytopenia include digoxin, erythromycin, heparin, penicillin, quinidine, sulfas and thiazides.
  • Infectious agents associated with secondary thrombocytopenia include equine infectious anemia andAnaplasma phagocytophilum.
  • Neoplasia.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Dunkel B (2013) Platelet transfusion in thrombocytopenic horses. Equine Vet Educ 25 (7), 359-362 VetMedResource.
  • McGovern K F, Lascola K M et al (2011) T-cell lymphoma with immune-mediated anemia and thrombocytopenia in a horse. J Vet Intern Med 25 (5), 1181-1185 PubMed.
  • McGurrin M K, Arroyo L G & Bienzle D (2004) Flow cytometric detection of platelet-bound antibody in three horses with immune-mediated thrombocytopenia. JAVMA 224 (1), 83-87 PubMed.
  • Clabough D L, Gebhard D, Flaherty M T et al (1991) Immune-mediated thrombocytopenia in horses infected with equine infectious anemia virus. J Virol 65 (11), 6242-6251 PubMed.
  • Humber K A, Beech J, Cudd T A et al (1991) Azathioprine for treatment of immune-mediated thrombocytopenia in two horses. JAVMA 199 (5), 591-594 PubMed.  
  • Sellon D C, Levine J, Millikin E et al (1996)Thrombocytopenia in horses - 35 cases. J Vet Intern Med 10 (3), 127-132 PubMed.