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Hematology

PLT Destruction

Overview of Thrombocytopenia Due to Increased Platelet Destruction

  • Definition: A group of disorders characterized by a decreased platelet count (<150 x 10^9/L) resulting from the accelerated destruction or consumption of platelets.

  • Key Distinctions:

    • Differentiating between increased destruction and decreased production is key. The bone marrow response (megakaryocyte number and activity) is essential for this distinction.
    • A normal, or even increased, megakaryocyte number in the bone marrow suggests that the problem lies in the destruction of platelets.

  • General Mechanisms:

    • Immune-Mediated Destruction: Antibodies or complement proteins bind to platelets, leading to their destruction by the mononuclear phagocyte system (MPS) or through complement-mediated lysis
    • Non-Immune-Mediated Destruction: Platelets are mechanically damaged or consumed in thrombotic microangiopathies (TMAs)
    • Sequestration: Platelets are trapped in the spleen due to splenomegaly

Key Laboratory Tests

  • Complete Blood Count (CBC):
    • To evaluate platelet count and other blood cell parameters
  • Peripheral Blood Smear Examination:
    • To assess platelet morphology and rule out other causes of thrombocytopenia
  • Direct Antiglobulin Test (DAT):
    • To rule out immune hemolysis
  • Coagulation Studies (PT, aPTT, Fibrinogen, D-dimer):
    • To rule out DIC
  • ADAMTS13 Activity Level:
    • To diagnose TTP
  • Stool Shiga Toxin Assay:
    • To diagnose typical HUS
  • HIT Antibody Testing:
    • To diagnose heparin-induced thrombocytopenia
  • Bone Marrow Aspiration and Biopsy:
    • To evaluate megakaryocytes and rule out other bone marrow disorders

Key Terms

  • Thrombocytopenia: Decreased platelet count (<150 x 10^9/L)
  • ITP (Immune Thrombocytopenic Purpura): Autoimmune destruction of platelets
  • TTP (Thrombotic Thrombocytopenic Purpura): Microangiopathic hemolytic anemia and thrombocytopenia due to ADAMTS13 deficiency
  • HUS (Hemolytic Uremic Syndrome): Microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury
  • DIC (Disseminated Intravascular Coagulation): Systemic activation of coagulation and fibrinolysis
  • Schistocytes: Fragmented red blood cells
  • ADAMTS13: A metalloprotease that cleaves von Willebrand factor (vWF)
  • Haptoglobin: Protein that binds free hemoglobin released into the plasma