HEMALAB2

• Platelets


  The primary cell involved in coagulation
• Platelet distribution

  • 2/3 circulation (70-80%)
  • 1/3 spleen (20-30%)
• Platelet maturity

  5 days
• Spleen


  Graveyard of RBCs
• Primary hemostasis (vascular side)

  1. Vascular injury

  2. Vasoconstriction

  3. Platelet adhesion

  4. Platelet activation

  5. Platelet secretion

  6. Platelet aggregation
• Platelet adhesion


  Platelet comes in contact with subendothelium (collagen, fibronectin) & attaches to some portion
• von Willebrand's disease (vWD)


  Results in impaired platelet adhesion if absent or abnormal form of von Willebrand factor
• von Willebrand factor


  Has glycoprotein IIb complex
• Bernard-Soulier syndrome


  Lacks GP1B
• GP1B


  Acts as receptor of von Willebrand Factor
• Platelet activation


  1. Function & morphological changes are made (discoid to sphere)

  2. Cyclooxygenase - Arachidonic acid - Prostaglandin endoperoxidase - Thromboxane A2
• Platelet secretion


  1. Platelet further change in shape due to contraction of microtubules

  2. Platelets move to the center of the platelet & fuse with other canalicular system then release granules
• Platelet granules - roles in hemostasis

  • HMWK (activates intrinsic coagulation pathway)
  • Fibrinogen (converts into fibrin clot formation)
  • Factor V (cofactor in fibrin clot formation)
  • Factor VIII (assist platelet adhesion into subendothelium to provide coagulation surface)
  • ADP (platelet aggregation)
  • Calcium (platelet aggregation)
  • Platelet factor IV (platelet aggregation)
  • Thrombospondin (platelet aggregation)
  • Serotonin (promotes vasoconstriction)
  • Thromboxane A2 (vasocontricts at injury site)
  • Platelet-derived growth (helps in smooth muscle for vascular repair)
  • Beta thromboglobulin (other system affected)
  • Plasminogen (plasmin precursor induces clot lysis)
  • A2-antiplasmin (plasmin inhibitor that inhibits clot lysis)
  • C1-esterase inhibitor (complement inhibitor)
• Platelet aggregation


  Following platelet release, the platelet stimulating agents bind to the platelets, causing them to adhere to one another
• Fibrinogen


  Necessary cofactor for platelet aggregation
• Glanzmann's thrombosthenia


  Decrease or absence of platelet membrane GP IIb-IIIa complex that acts
• Platelet count (normal value)

  150,000-400,000 uL (150-400 x 10^9 a/L)
• Conditions with thrombocytosis


  • Polycythemia vera
  • Idiopathic thrombocythemia
  • Chronic myelogenous leukemia
  • Splenectomy
• Conditions with thrombocytopenia


  • Aplastic anemia
  • Acute leukemia
  • Pernicious anemia
  • Chemotherapy & radiation
• Pernicious anemia


  Vitamin B12 deficiency caused by Diphyllobothrium latum
• Normal platelet count + Prolonged bleeding time


  Qualitative platelet abnormality, primary vascular abnormality, von Willebrand's disease
• Low platelet count + Normal bleeding time


  Autoimmune thrombocytopenia
• Low platelet count + Very prolonged bleeding time


  Quantitative & qualitative platelet deficiency
• Platelet aggregation test


  Assay to determine alteration to platelet function
• Platelet adhesiveness (Salzmann)


  Measures ability of platelets to adhere in glass surfaces, found to be decreased in von Willebrand's disease, normal value: 26-60%
• Clot retraction time


  Requires normal number of functioning platelets, calcium, antiplasmin & normal fibrinogen level, must also have interaction between platelet with fibrinogen & thrombin
• Castor oil/Hirschboeck method


  Formation of dimping/droplet-like serum on surface of blood drop, normal value: 14-45 mins
• Stefanini method


  Needs 3-5ml blood at 37C, normal value: appreciable within 1 hr, complete within 18-24 hours
• McFarlane method


  5ml blood at 37C, CRT = volume serum/total volume x100, normal value: 44-67%
• Capillary fragility test


  Degree of thrombocytopenia will correlate with the test as well as bleeding time, positive test: 1+ few petechiae, 2+ many petechiae, 3+ multiple petechiae, 4+ confluent petechiae
• Bleeding time (Duke method)


  Primary hemostasis screening test for platelet & vascular function, normal value: 2-4 mins
• Bleeding time (Ivy method)


  BP cuff is set to 40 mmHg, a calibrated spring-loaded lancet is triggered in the forearm distal to the antecubital crease, then wound is blotted every 30secs, normal value: 3-6 mins
• Secondary hemostasis


  Involves coagulation factors also known as enzyme precursors & zymogens, interaction of coagulation factors in forming stable fibrin clot
• Zymogens

  • II, VII, IX, X, XI, XII, & Prekallikrein
• Serine proteases

  • IIa, VIIa, IXa, Xa, XIa, XIIa & Kallikrein
• Cofactors


  Assist in the activation of zymogens, includes V, VIII, tissue factor, HMWK
• Coagulation factors are produced mostly in the liver and circulate in their inactive form
• PT & APTT


  Requested for suspected cirrhosis
• Clotting time (capillary method)


  Measures free forming blood clot after blood has been drawn, normal value: 2-4 mins
• Clotting time (whole blood/Lee&White method)


  Uses 3 glass tubes & kept on a water bath (37C), tilted every 30secs until blood fully clots, record an average time of 3 tubes, normal value: 5-15 mins