hema lec 2

• Platelet count


  Normal range in humans is 150-400 x 109/L
• Platelet count below 50x109/L


  Increases risk of pathologic hemorrhage
• Causes of increased platelet destruction or reduced platelet production

  • Inadequate platelet production
  • Increased destruction of platelets
  • Platelet trapping
  • Abnormal platelet distribution/pooling
• Pseudothrombocytopenia


  • Platelet agglutination
  • Platelet satellitism
  • APLAGP IIa-IIIa Antagonists
  • Giant Platelets
  • Miscellaneous associations
• Accelerated platelet destruction


  • Immune (Idiopathic) Thrombocytopenic Purpura
  • Neonatal Alloimmune Thrombocytopenia
  • DIC
  • SLE
  • TTP/HUS
  • Post-transfusion Purpura
  • Drug-induced
  • Infections
• Impaired platelet production


  • Drugs
  • Mediterranean Macrothrombocytopenia
  • Paris-Trousseau Syndrome
  • Wiskott-Aldrich Syndrome
  • Fanconi Anemia
  • Aplastic Anemia
  • Megaloblastic Anemia
  • Marrow Infiltration
  • MYH9 Related Thrombocytopenia Syndromes
• Platelet trapping


  • Kasabach Merrit Syndrome
• Abnormal platelet distribution/pooling


  • Splenomegaly
  • Hypersplenism
  • Massive Transfusion
• Drug-induced thrombocytopenia


  • Affects only a small percentage of patients taking a particular drug, and though not usually severe, it can be fatal
  • Genetic or environmental factors both influence susceptibility to drugs
• Mechanisms of drug-induced thrombocytopenia

  • Dose-dependent myelosuppression
  • Immune destruction of the platelets
• Heparin-induced thrombocytopenia (HIT)


  • An immune-mediated disorder caused by antibodies that recognize a neoepitope in platelet factor 4 that is exposed when platelet factor 4 binds heparin
  • Results in activation of platelets and the coagulation cascade and, ultimately, thrombosis
  • Affects up to 5 percent of patients exposed to heparin
• Other drugs that can cause thrombocytopenia


  • Sulfamethoxazole
  • Penicillin
  • Gold salts
  • Quinidine
  • Quinine
  • Diazepam
  • Lithium
  • Amiodarone
  • Acetazolamide
  • Amphotericin B
• Neonatal thrombocytopenia


  • Caused by maternal antibodies crossing the placenta and destroying fetal platelets
  • Most common antigen is HPA-1a
  • Usually resolves within 3 weeks (maximum 3 months) after delivery
  • In severe cases, purpura and hemorrhages are evident at birth or manifest within a few hours
• Other causes of neonatal thrombocytopenia

  • Thrombocytopenia with absent radius syndrome
  • Infections
  • Drug induced
  • Congenital megakaryocytic hyperplasia
  • Congenital leukemia
• Post-transfusion purpura


  • Rare with sudden onset
  • Bleeding occurs 7-10 days after blood transfusion
  • Caused by donor platelets (HPA-1a antigen) destroying the patient's already sensitized platelets
  • Treated with IV gamma globulins and plasmapheresis
• Disseminated intravascular coagulation (DIC)

  • An acute, subacute, or chronic thrombohemorrhagic disorder
  • Occurs as a secondary complication in a variety of diseases
  • Caused by the systemic activation of the coagulation pathways, leading to the formation of thrombi throughout the microcirculation
• Conditions that can lead to DIC

  • Obstetric complications
  • Infections
  • Neoplasms
  • Massive tissue injury
  • Miscellaneous (acute intravascular hemolysis, snakebite, giant hemangioma, shock, heat stroke, vasculitis, aortic aneurysm, liver diseases)
• Characteristics of DIC


  • Intravascular activation of extrinsic pathway of coagulation with generation of thrombin and fibrin
  • Reduction in level of endogenous anticoagulants (antithrombin, protein C)
  • Suppression of fibrinolytic system which causes delayed and inadequate removal of fibrin
• Types of DIC


  • Acute/Decompensated DIC
  • Chronic/Compensated DIC
• Acute/Decompensated DIC


  • Rapid and extensive activation of coagulation leading to significant bleeding from consumption of coagulation factors and widespread microvascular thrombosis
  • Sudden onset of spontaneous bleeding from multiple sites
• Laboratory findings in Acute/Decompensated DIC

  • Low or falling platelet count
  • Prolonged PT and aPTT
  • Low or falling fibrinogen levels
  • Low plasma levels of coagulation inhibitors
  • Presence of schistocytes on blood smear

  
• Chronic/Compensated DIC


  • Slow activation of coagulation in small amounts with slow consumption of coagulation factors
  • Coagulation factors are normal or increased
  • Clinical features are minimal or absent
  • Laboratory abnormalities are the only evidence of DIC
• Laboratory findings in Chronic/Compensated DIC

  • Platelet count normal or slightly reduced
  • PT and aPTT are normal
• Pseudothrombocytopenia or spurious thrombocytopenia


  • Uncommon phenomenon caused by ex vivo agglutination of platelets
  • Leads to platelet clumping, causing reduced platelet counts on automated cell counters
• Causes of pseudothrombocytopenia


  • Use of EDTA anticoagulant
  • Multiple myeloma
  • Presence of platelet cold agglutinins
• Antibody-induced platelet agglutination


  • Caused by ex vivo antibodies or platelet activation during collection
  • Antibodies recognize modified or exposed platelet membrane glycoproteins when calcium is chelated
  • Antibodies are typically of the IgG type, but IgM and IgA can also be involved
• Anticoagulants that can cause antibody-induced platelet agglutination

  • EDTA
  • Sodium citrate
  • Sodium oxalate
  • Acid citrate dextrose
  • Heparin
• Preventing antibody-induced platelet agglutination

  • Taking the blood sample at 37°C
  • Pretreatment of donor platelets with aspirin or prostaglandin E1
  • Use of monoclonal antibodies against GP IIb/IIIa
• Platelet satellitism


  • Antibodies directed against GPIIb/IIIa react with Fc receptor III (FcRIII) on leukocytes, causing platelets to attach to neutrophils and monocytes
  • Neutrophils are most commonly involved, but monocytes can also be involved
  • These antibodies are naturally occurring and their presence does not clearly correlate with any clinical situation, disease or drug
• Antiphospholipid antibodies (APLA)


  • Some anti-platelet antibodies from patients with pseudothrombocytopenia cross-react with negatively charged phospholipids and exhibit anticardiolipin activity
  • These antibodies can bind to antigens modified by EDTA on the platelet membrane and cause platelet clumping
• MYH9-related thrombocytopenia syndrome


  • Autosomal dominant macrothrombocytopenia with mutations in the MYH9 gene
  • MYH9 gene encodes NMMHC-IIA, an important cytoskeletal contractile protein in hematopoietic cells
  • Defect in platelet number is likely due to a defect in platelet maturation from proplatelets
  • Includes a triad of thrombocytopenia, macrothrombocytes, and Dohle body-like inclusions in neutrophils
• NMMHC-IIA protein


  • Important cytoskeletal contractile protein in hematopoietic cells
• Mutation in MYH9 gene


  Produces a highly unstable protein with abnormal organization of the megakaryocyte cytoskeleton
• Defect in platelet number is likely defect in platelet maturation from proplatelets, as when MYH9-deficient stem cells were differentiated to megakaryocytes they produced proplatelets normally
• Syndromes include


  • Thrombocytopenia
  • Macrothrombocytes
  • Dohle body like inclusions
  • Other syndromes
• Hallmark feature of MYH9-related disorders

  • Neutrophilic inclusions that appear blue with Wright-Giemsa stains, corresponding to cytoplasmic aggregates of NMMHC-IIA
• Mediterranean macro thrombocytopenia


  Mild congenital thrombocytopenia with autosomal dominant pattern of inheritance
• Many patients share clinical and molecular features with heterozygous Bernard-Soulier syndrome phenotype
• Linkage analyses


  Reveal heterozygous Ala156Val missense substitution in the GP Ib gene (also known as Bolzano mutation), which is also present in patients with Bernard-Soulier syndrome
• Clinical manifestations


  Variable, with severity of bleeding related to both platelet number and function