Primary Hemostasis: Components, Events, and Disorders

PRIMARY HEMOSTASIS Components:  Vascular System – arteries, capillaries and veins - Prevents bleeding by: 1. Diverting blood flow from damaged vessels 2. Initiating contact activation of platelets with aggregation 3. Activating the coagulation system - Contains varying amounts...

PRIMARY HEMOSTASIS Components:  Vascular System – arteries, capillaries and veins - Prevents bleeding by: 1. Diverting blood flow from damaged vessels 2. Initiating contact activation of platelets with aggregation 3. Activating the coagulation system - Contains varying amounts of fibrous tissue (collagen, elastin, smooth muscle cells, fibroblasts)  Platelets – productions is influenced by THROMBOPOIETIN produced in the liver or kidneys - Maturation time from the blast stage to platelet formation is typically 5 days - Normal marrow contains approximately 15 million megakaryocyte. (equates to ~ 5 to 10 megakaryocytes per 10× power field when bone marrow smears are microscopically examined) - Normal circulation life of a platelet is 8 to 10 days - Platelets are removed by macrophage in the liver and spleen or by active use in daily coagulation mechanisms. - Circulating platelets are distributed between the spleen and blood: a. 1/3 in spleen b. platelet count is higher in patients without a spleen and lower in patients with splenomegaly enlarged spleen. - Regulation of the platelet count a. Under normal conditions the platelet count (or mass) is constant, even with active use. This indicates a feedback system that adjusts production to consumption. (1) Rebound thrombocytopenia occurs after platelet transfusion. (2) Rebound thrombocytosis occurs after platelet depletion. b. Feedback stimulus results in an increased megakaryoblast endomitosis, which increases platelet volume and number. It also affects committed unipotential stem cells, which results in more megakaryoblast. Events:  Vasoconstriction – 1st response to injured vessel - Initiated by serotonin and thromboxane A derived from 2 platelets and endothelial cells  Formation of Primary Hemostatic Plug or Platelet Plug  Adhesion – platelet adherence to exposed subendothelial surface* - *collagen – in vivo & *glass – in vitro - Occurs within 1 to 2 mins after a break in the endothelium - Occurs in the presence of vWF (receptor for vWF: Gp1b)  Activation – morphologic and functional changes in platelets - Agonists that lead to platelet activation are varied & include: o Nucleotide (ADP) o Lipids (TxA2, platelet-activating factor) o A structural protein (collagen) o Proteolytic enzyme (thrombin) - Arachidonic acid – a substrate that is converted to TxA2 by cyclooxygenase - Functions of TxA2: vasoconstrictor & stimulates platelet secretion  Secretion – release of platelet granules - Alpha granules (platelet factor, platelet-derived GF, platelet fibrinogen, factor V, vWF, b-thromboglobulin, thrombospondin, fibronectin & platelet albumin) - Dense granules: Ca – involved in all steps of coagulation (except the contact factor of the intrinsic pathway of secondary hemostasis) ADP – stimulates platelet aggregation Serotonin – vasoconstrictor  Aggregation – platelet attachment to each other - Requires fibrinogen & Ca (receptor for fibrinogen: GpIIb-IIIa Glycoprotein Receptors: GpIb – receptor for vWF GpIIb-IIIa – receptor for fibrinogen GpVa – receptor for thrombin  End result of these processes is formation of primary hemostatic plug or platelet plug  In summary, events in primary hemostasis include: o VASOCONSTRICTION o PLATELET ADHESION o PLATELET ACTIVATION o PLATELET SECRETION o PLATELET AGGREGATION o PRIMARY HEMOSTATIC PLUG or PLATELET PLUG FORMATION Disorders of Primary Hemostasis  can be a defect in the vascular components or platelet (quantitative or qualitative) DISORDER REMARKS HEREDITARY CONNECTIVE TISSUE DEFECTS EHLERS-DANLOS SYNDROME Increased vascular fragility; lack of peptidase that converts procollagen to collagen PSEUDOXANTHOMA ELASTICUM Elastic fibers in small arteries are calcified & structurally abnormal ACQUIRED CONNECTIVE TISSUE DEFECTS SCURVY Defect in collagen synthesis due to deficiency of Vit C or ascorbic acid SENILE PURPURA Degradation of collagen and elastin HEREDITARY ALTERATIONS OF VESSEL WALL SYNDROME HEREDITARY HEMORRHAGIC TELANGIECTASIA Most common inherited vascular disorder; blood (OSLER-WEBER-RENDU DISEASE) vessel walls are thin and lack smooth muscle CONGENITAL HEMANGIOMATA (KASABACH- Blood vessel tumor MERRITT SYNDROME) ACQUIRED ALTERATIONS OF VESSEL WALL SYNDROME DIABETES MELLITUS Large vessels may become atherosclerotic and capillary basement membrane may thicken thus blocking normal blood flow AMYLOIDOSIS Deposition of fibrillar protein (amyloid) causing vessel obstruction ENDOTHELIAL DAMAGE AUTOIMMUNE VASCULAR PURPURA Drug-induced purpura Quinine, procaine, penicillin, aspirin, sulfonamides, sedatives, coumarins Allergic (HENOCH-SCHÖNLEIN PURPURA) Henoch purpura: associated with abdominal pain secondary to GI bleeding Schönlein purpura: associated with joint pain INFECTIOUS PURPURA Bacteria, viruses and parasites Platelet Disorders - Quantitative  Thrombocytopenia – decrease in the no. of circulating platelet - Decrease Production o aplastic anemia/ Pancytopenia – decrease RBC, WBC & platelets (Congenital: Fanconi’s anemia; Acquired: exposure to radiation, drugs (Chloramphenicol) & benzene) o Drug Toxicity – Chlorothiazide (selective suppression of the megakaryocyte) o Myelophthisic process – space-occupying lesion in the bone marrow such as metastatic tumor, fibrosis, or leukemia - Increased Loss or Destruction  Dilutional Loss – extensive blood transfusion is often accompanied by thrombocytopenia, and the degree of which is directly proportional to the no. of units transfused  DIC – mass consumption of platelets  ITP – autoantibody directed against platelet o Acute ITP – most common cause of thrombocytopenia in children; acquired after a viral illness such as measles, chickenpox, rubella or infectious mononucleosis o Chronic ITP – occurs in adults - Increased Platelet Sequestration by Spleen  Splenomegaly – 50 – 90% of platelets may be sequestered  Thrombocytosis – increase in number of circulating platelets - Primary (Autonomous) – uncontrolled proliferation of platelets Characteristics of myeloproliferative disorders o Polycythemia vera PV o Essential thrombocytopenia (ET) o Chronic Myelogenous Leukemia (CML) o Myelofibrosis with myeloid metaplasia (MMM) - Secondary (Reactive) – thrombocytosis is usually transient Iron deficiency – iron inhibits thrombopoietin Hemolytic anemias & acute blood loss – due to rapid blood regeneration Splenectomy – increase platelet count is noted 1 to 10 days after splenectomy and peaks 1 to 3 weeks later Platelet Disorders - Qualitative  Hereditary o Platelet Adhesion Disorders  Bernard-Soulier Disease – lacks GpIb; associated w/ giant platelets  Von Willebrand Disease – lacks vWF; treated w/ cryoprecipitate o Platelet Aggregation Disorders  Glanzmann’s Thrombasthenia – lacks GpIIb-IIIa complex RESULTS in PLATELET AGGREGATION TEST Bernard-Soulier & vWD – Normal: ADP, Collagen & Epinephrine Abnormal: Ristocetin Glanzmann’s Thrombasthenia – Normal: Ristocetin Abnormal: ADP, Collagen & Epinephrine  Hereditary (cont.) o Platelet Secretion Disorders  ALPHA GRANULE DEFICIENCY Gray Platelet Syndrome - Platelets are large and gray or blue-gray in color - Dense tubular system which is storage site for Ca and cyclooxygenase is abnormal  DENSE GRANULE DEFICIENCIES Hermansky-Pudlak – Triad of tyrosinase-positive oculocutaneus albinism, accumulation of ceroid-like pigment in macrophages and bleeding tendencies Chediak-Higashi – characterized by albinism, recurrent infections and giant lysosomes in all granule-containing cells Wiskott-Aldrich Syndrome – Triad of thrombocytopenia, recurrent infections and eczema; platelets are small and have abnormal cellular membrane  Acquired o Uremia – accumulation of toxic metabolites o Paraproteinemias – coating of platelet membrane with abnormal protein o AML – characterized by abnormal megakaryocyte o Myeloproliferative disorders o Drugs - Aspirin (and other NSAIDs) – result in a platelet dysfunction by irreversible inactivation of the cyclooxygenase enzyme and the resultant decrease in TxA2 formation - Carbenicillin – the most potent of the penicillin group of antibiotics capable of affecting platelet function Basic Terminology for Clinical Findings in Bleeding Disorders  Petechiae – purplish red pinpoint hemorrhagic spots (3 cm) in which blood escapes into large areas of skin and mucous membranes, but not into deep tissues  Epistaxis – nosebleed  Hemarthrosis – leakage of blood into joint cavities  Hematemesis – vomiting of blood  Hematoma – swelling or tumor in the tissues  Hematuria – red blood cells in urine  Hemoglobinuria – hemoglobin in urine  Melena – stool with dark red or black blood  Menorrhagia – excessive menstrual bleeding Laboratory Tests for Primary Hemostasis  Platelet Count  NV: 150 to 450 x 109/L  Methods: Manual & Automated  Significant bleeding does not occur until platelet count is less than 60 x 109/L - 20 to 60 x 109/L = minor bruising, menorrhagia & post-operative or post- traumatic bleeding - Below 20 x 109/L = spontaneous bleeding into skin & mucous membrane (most serious site of bleeding – CNS)  Bleeding Time  In vivo measure of primary hemostasis  NV: 2 to 9 mins (Steininger)  Methods: - Duke Method – fingertip or earlobe - Ivy Method – pressure cuff at 40 mmHg  As long as platelet function is normal, template bleeding time is not increased when platelet counts are greater than 100 x 10 9/L - When count falls below this, the degree to which bleeding time is prolonged is inversely proportional to the decrease in platelet count  Platelet Adhesiveness  Glass Bead Retention Test  Platelet Adhesiveness in vivo  Platelet Aggregation  In vitro test to determine the ability of platelets to aggregate with certain agonist: Epinephrine, ADP, collagen, ristocetin  Platelet-rich plasma (PRP) + agonist  O.D. monitored  PRP is prepared by centrifugation at 200 x g for 10 minutes  Tube used: 75 mm plastic tube  Clot Retraction Time  Within 1 hr after whole blood is allowed to clot in a clean glass tube at 37oC, the clot will begin to shrink and retract from the walls of the tube.  Clot retraction depends on normal numbers of contractile platelets, Ca & ATP & a normal concentration of fibrinogen  Castor Oil/ Hirschboeck Method - Formation of dimpling/ droplet-like serum on the surface of blood drop - NV: 15 to 45 minutes  Clot Retraction Time (cont.)  Stefanini Method - Uses 3 to 5 mL blood at 37oC - Measured at 1/2/16/18/24 hours - NV: retraction begins within 1 hr & completes within 18 to 24 hrs  MacFarlane Method - Uses 5 L blood at 37oC for 1 hr - CRT = volume or serum/total volume x 100 - NV: 44 to 67%  Usually abnormal when platelet count is below 60 x 10 9/L  Capillary Fragility Test/ Rumpel-Leede Test/ Tourniquet Test  Correlates with the degree of thrombocytopenia  100 mmHg or midway of the systolic and diastolic pressure for 5 min and after 15 to 30 min, count petechiae  Decrease platelet – increase petechiae  This test should not be repeated on the same arm for 7 days!!! Grade Petechiae Remarks 1+ 0 – 10 Few petechiae on the anterior surface of the arm 2+ 10 – 20 Moderate petechiae on the anterior surface of the arm 3+ 20 – 50 Many petechiae on the arm & at the back of the hands 4+ >50 Confluent petechiae on the arm & at the back of the hands