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General Laboratory: Hemostasis: Basic Overview Online Training

Hemostasis is a complex process which includes coagulation factors, platelets and the vessels. The goal of Hemostasis is to maintain a delicate balance between these systems to avoid excessive bleeding and prevent a thrombotic event.

Welcome to the Hemostasis Overview course. Blood in its liquid state is maintained within the vascular system and delivers oxygen and nutrients to all of the body’s cells and organs. When damage occurs to a blood vessel, through a series of reactions which include platelets, coagulation factors, and the vascular system a clot is formed. Once the vessel injury is repaired the clot needs to be removed so blood can circulate freely in its fluid state. This is possible via the fibrinolytic system. The body’s ability to maintain this delicate balance between blood in a liquid and solid form is called hemostasis. Maintaining this balance requires several different systems to work together to prevent excessive bleeding or clotting.  Either condition can be life threatening. Effective treatment of bleeding and clotting disorders depends on the proper identification of the abnormality.  The hemostasis laboratory plays an important role in diagnosing, monitoring and in the treatment of bleeding and clotting disorders. Select Next to continue. Identify common tests performed in Hemostasis Identify hemostasis disease states and anticoagulant therapies Identify the different pathways of the coagulation cascade Identify the process of hemostasis After completing this course, you will be able to: Select Next to continue. Congratulations. You have completed the Hemostasis Laboratory Overview.  Once you have reviewed the content on this page, you may proceed to the assessment portion of the course. In this course, you have learned how to: Recognize the process of hemostasis The process of hemostasis involved 4 systems:  the vascular system, platelets, coagulation factors and the fibrinolytic system. The vascular response includes collagen exposure at the site of injury and vasoconstriction to reduce blood loss. Platelets are activated and aggregate at the site of injury, creating a platelet plug.  This process is called primary hemostasis. The coagulation cascade is activated resulting in a stable fibrin clot at the site of the injury.  This process is called secondary hemostasis. Once the injured vessel is healed the fibrinolytic system breaks down the clot and prevents clot formation beyond the site of injury. Identify the different pathways of the coagulation cascade The coagulation cascade is a series of enzymatic reactions that result in a stable fibrin clot to stop bleeding and consists of three pathways. The intrinsic pathway involves factors XII, XI, IX, and VIII and is initiated by contact with the surface of the injured blood vessel. The extrinsic pathway involves factor VII and is initiated by tissue thromboplastin released into the blood stream when there is vessel damage. The intrinsic and extrinsic pathways converge into the common pathway which includes factors V, X, II (prothrombin) and I (fibrinogen). Recognize hemostasis disease states and anticoagulant therapies Hemostasis disorders can cause excessive bleeding or excessive clotting and can range from mild to life threatening. Bleeding disorders such as von Willebrands Disease, factor deficiencies (Hemophilia) or Vitamin K deficiencies reduce the patient's ability to clot and can result in excessive bleeding. Inherited or acquired clotting disorders increase the patient's ability to form clots and can cause Deep Vein Thrombosis or Pulmonary Embolism. Heparin therapy or Oral Anticoagulant therapy is used to reduce the patient’s risk of a thrombotic (clotting) event and must be monitored carefully. Recognize common tests performed in Hemostasis   The Prothrombin Time (PT) evaluates the effectiveness of the extrinsic and common pathways of the coagulation cascade.  The PT is used as a screening test to evaluate a patient’s ability to clot and to monitor Oral Anticoagulant Therapy such as warfarin therapy. The activated Partial Thromboplastin Time (APTT) evaluates the effectiveness of the intrinsic and common pathways of the coagulation cascade.  The APTT is used as a screening test to evaluate a patient’s ability to clot and to monitor heparin therapy. The Fibrinogen assay evaluates the amount of fibrinogen available to convert into fibrin and create a fibrin clot.  The Fibrinogen assay can help determine the severity of Disseminated Intravascular Coagulation (DIC) where a patient clots uncontrollably consuming all of his coagulation factors. A quantitative D-dimer assay such as the INNOVANCE® D-Dimer Assay measures the amount of D-dimer in a patient sample.  D-dimer is created by the breakdown of a stable fibrin clot during fibrinolysis and can help with the diagnosis of Deep Vein Thrombosis or Pulmonary Embolism. Factor Assays such as the Factor VIII assay measures the activity of specific factors in the coagulation cascade and can help diagnosis and monitor factor deficiencies such as Hemophilia. The Platelet Function Assay (PFA) evaluates the platelets ability to adhere and aggregate, creating a platelet plug during primary hemostasis.  The PFA can help diagnose platelet dysfunction such as von Willebrands Disease or Aspirin Ingestion. Select Next to continue.       During normal hemostasis, if a blood vessel is injured, the following interdependent systems are called to action: Vascular system Platelets Blood coagulation factors Fibrinolytic system The Hemostasis Process Learn about the Hemostasis process. Checklist TitleChecklist TypeChecklist ContentHemostasis ProcessHTML    Select the Play arrow to watch the hemostasis process.  During normal hemostasis, the following systems work together: Vascular system Platelets Blood coagulation factors Fibrinolytic system Select each checkbox to learn more about the Hemostasis process. Vascular ResponseHTML   Select the play arrow to watch the vascular response. Under normal conditions, blood remains liquid and flows freely through the body’s blood vessels.  The blood vessels are lined with a thin layer of endothelial cells that prevents the blood from adhering to the vessel walls and prevents clot formation. During vessel injury or in some disease states, this endothelial cell lining is disrupted.  This initiates vasoconstriction in which the vessel narrows to restrict the blood flow to the site of the injury.  When the endothelial cells are disrupted they also expose the flowing blood to the sub layer of the vessel lining called the collagen layer.  The exposure of the collagen layer and release of other substances from the damaged tissue begins a series of events that quickly seal the damaged area of the vessel and prevent excessive blood loss. When a blood vessel is damaged, the following vascular reactions can occur: Vasoconstriction - Blood vessels narrow to reduce blood flow to a damaged area. Collagen exposure - The collagen layer is part of the sub-endothelium of blood vessels. Platelets and clotting factors activate when they come in contact with exposed collagen of damaged blood vessels. The Platelet's RoleHTML   Select the play arrow to watch the platelets' role in hemostasis. Platelets that are circulating in the blood are the first to respond to the collagen exposure.  Very quickly, the platelets begin to adhere to the site of the injury and activate.  Activated platelets change shape and become sticky.  They also release a series of chemicals that cause additional platelets to activate and aggregate or stick together in the damaged area.  Platelet aggregation causes a fragile plug to form that stops blood from escaping through the damaged vessel lining.  This platelet plug formation is called primary hemostasis.  The Platelet’s Role Contact with exposed collagen causes platelet activation and adhesion at the site of the injury. Activated platelets release various substances and initiate platelet aggregation in the damaged area. Platelet aggregation causes the formation of a platelet plug to stop bleeding in the damaged area. Activation of the Coagulation CascadeHTML   Select the play arrow to watch the activation of the coagulation cascade. The platelet plug is extremely fragile and needs to be stabilized to effectively prevent bleeding.  This involves interactions of coagulation proteins resulting in formation of fibrin which stabilizes the platelet plug. Platelets play a role by secreting phospholipid materials which serve as the basis for the activation of the coagulation cascade.     The coagulation cascade is a series of sequential reactions involving the coagulation factors that eventually create a stable fibrin clot at the site of injury.  Fibrin is a very sticky mesh that adheres to the damaged vessel trapping platelets and other blood cells in a solid form.  The formation of the fibrin clot is called secondary hemostasis. The coagulation factors consist of plasma proteins, calcium and a material released by the vessel when damaged called thromboplastin. Most coagulation factors are made in the liver and circulate freely in the blood stream in an inactive form. Coagulation factors are: Made up of plasma proteins, except for calcium and thromboplastin Produced in the liver, except for Factor VIII Circulated in plasmain an inactive form as enzyme precursors, or as catalysts for other enzymatic reactions Role of the Fibrinolytic SystemHTML   Select the play arrow to watch the fibrinolytic system. After the injury is repaired, the fibrin clot is dissoved by a process called Fibrinolysis. During fibrinolysis the stable fibrin clot is broken down into smaller pieces by fibrinolytic factors.  The fibrinolytic system is also very important in keeping clots from forming beyond the site of the injury once the platelets and coagulation factors are activated. Plasminogen circulates in the blood. When plasminogen is activated, it is converted to plasmin. Plasmin is responsible for breaking down the stable fibrin clot.  The two main components of the Fibrinolytic system are: Plasminogen is a plasma protein circulating in the blood.  When the initial vessel damage occurs, plasminogen is activated to its enzymatic form, Plasmin. Plasmin breaks down both fibrinogen that circulates freely in the blood stream and the stable fibrin clot created during the coagulation cascade.   Products of FibrinolysisHTML   Select the play arrow to watch the fibrinolytic system. The products of Fibrinolysis are: Fibrinogen Degradation Products Fibrin Degradation Products D-dimer Fibrinogen degradation products are created when plasmin breaks down fibrinogen molecules, the precursors of fibrin that circulate freely in the blood stream.  Fibrin degradation products are created when plasmin breaks down stable fibrin clots.  Both products are referred to as FDPs. D-dimer is a specific type of degradation product that is created strictly when plasmin breaks down a stable fibrin clot, not by the breakdown of fibrinogen.  Therefore the presence of D-dimer molecules in a patient’s blood indicate that a stable fibrin clot was formed and broken down by plasmin.   Main Components of the Hemostasis ProcessHTML Congratulations.  You have just learned the main components of the Hemostasis Process. Injured Vessel Vascular System Platelets Blood Coagulation Factors Fibrinolysis When complete, select the X in the upper-right corner to close the window and continue. The coagulation cascade consists of three pathways: Intrinsic Pathway Extrinsic Pathway Common Pathway The Coagulation Cascade Learn about the Coagulation Cascade pathways. Checklist TitleChecklist TypeChecklist ContentCoagulation CascadeHTML Select each checkbox to learn more about the Coagulation Cascade. There are three pathways that constitute the Coagulation Cascade: Instrinsic Pathway Extrinsic Pathway Common Pathway  Intrinsic PathwayHTML   Select the play arrow to view the video illustration. Factors involved: Factor XII Factor XI Factor IX Factor VIII Extrinsic PathwayHTML   Select the Play arrow to view the video illustration. Factor involved:  Factor VII The Common PathwayHTML   Select the Play arrow to view the video illustration. Factors involved: Factor V Factor X Prothrombin (Factor II) Fibrinogen (Factor I) CascadeHTML   Select the Play arrow to view the video illustration. The Intrinsic Pathway and Extrinsic Pathway occur simultaneously activating the common pathway. When complete, select the X in the upper-right corner to close the window and continue. In the following section, you will learn about Hemorrhagic disorders and thrombotic events, both of which can be congential or acquired. Hemostasis Disorders are classified as: Hemorrhagic Disorders Thrombotic Events Anticoagulant Therapies will also be discussed. Select Next to continue. Bleeding Disorders can occur for various reasons and can lead to hemorrhage. Select each tab to learn about the more common bleeding disorders. Many patients have individual factor deficiencies that can cause lifelong bleeding disorders. Some factor deficiencies are prevalent in certain ethnic groups i.e., Factor XI is found in Ashenaki Jews. Patients may also develop inhibitors (antibodies) to factors, which can also cause life threatening bleeding. These are the result of the formation of IgG antibodies. Vitamin K is essential for the production of many coagulation factors. Depending on the extent of deficiency, this can lead to bleeding problems in the patient. Hemophilia is an inherited bleeding disorder caused by a Factor VIII or Factor IX deficiency and can be present in one of several forms. The most severe hereditary hemophilic disorder is a deficiency of Factor VIII. Hemophilia A, an X-linked recessive gene, affecting male offspring of females who carry the gene. Signs can vary from mild (trauma results in prolonged bleeding) to severe (spontaneous excessive bleeding in the tissues). Von Willebrand disease is the most commonly inherited coagulation disorder. This is a result of a deficiency or functional abnormality in Factor VIII-von Willebrand factor causing interference with platelet adhesion. Clinical signs are variable from prolonged bleeding to massive bleeding. Select Next to continue. Thrombosis or clotting events are more common than bleeding disorders and can be very severe. Select each tab to learn about the most common clotting events. Thrombotic Event: Deep Vein Thrombosis (DVT) Most commonly, clots develop in the deep veins of the legs, pelvis or upper extremities. If they remain in the leg, they create problems such as phlebitis which can be mild to severe. If the clot is dislodged, it may travel towards the heart, lungs or brain. Thrombotic Event: Pulmonary Embolism (PE) When a thrombus in the deep veins dislodges, it can travel to the heart where the veins are larger and the emboli do not get lodged. The clot can travel through the heart and to the lungs, following the normal blood flow pathway. In the lungs, the vessels are smaller. The clot may finally get lodged there. This is called pulmonary embolism (PE). If the blockage is large or a result of many clots and goes un-detected, it can be fatal. Thrombotic Event: Thrombotic Strokes When a thrombus in the deep veins dislodges, it can travel throughout the body, following normal blood flow.  When that clot travels far enough to reach the brain, a thrombotic stroke occurs. Thrombotic Event: Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation (DIC) is a serious condition in which widespread thromboses lead to massive internal bleeding when all of the coagulation factors become consumed. Bleeding and clotting occurs due to the simultaneous formation of thrombin and plasmin. Patients can develop DIC which causes widespread damage to the vascular system from injuries such as those incurred from an automobile accident. Certain bacterial and viral infections and drug reactions also can lead to DIC. Select Next to continue. In cases of an inappropriate clot formation, patients can be treated with anitcoagulants to prevent additional clots from forming. Select each tab to learn about each type of anticoagulant therapy. In patients with serious clotting disorders such as acute coronary syndrome, pulmonary embolism and deep vein thrombosis, heparin therapy typically is the first response to prevent further clot formation.  Heparin, administered intravenously, is fast acting, but cannot dissolve clots that already exist. However, by preventing the activation of Factor X and thrombin, heparin stops additional clots from developing. Oral anticoagulants are used as a long term therapy to prevent reoccurrences of a thrombotic episode. They inhibit the patient’s ability to form clots by reducing the function of Vitamin K, rendering the Vitamin K dependent factors (II, VII, IX and X) non-functional. Aspirin, along with its pain relieving properties, has the ability to interfere with platelet activation.  In coronary heart disease, the blood vessels become lined with cholesterol.  These “plaques” of cholesterol can initiate platelet adhesion and aggregation. Aspirin reduces the platelets ability to activate and adhere to the vessel walls, reducing the risk of clot formation, heart attack and stroke. Select Next to continue. During Hemostasis testing, the patient’s ability to form a clot is evaluated. When the specimen is collected, a light blue top tube containing 3.2% sodium citrate anticoagulant is used. Sodium citrate prevents the patient’s blood from clotting in the tube. A 9:1 ratio of blood to citrate must be maintained. If the tube is not properly filled or has the incorrect blood:citrate ratio, it may affect test results. Most hemostasis testing is performed on platelet poor plasma. Platelets are a source of phospholipid and reagents contain phospholids, thus, if platelets are present in the plasma they may falsely shorten results. Normal plasma contains all of the coagulation factors. Note: Most hemostasis analyzers detect clot formation optically.  When the sample and reagent are added to a reaction vessel, the solution begins as a liquid and light passes easily through the solution.  As the fibrin clot begins to form the solution changes from a liquid to a solid which decreases the amount of light that can pass through the reaction vessel.  An algorithm is then used to determine the clot time based on the pattern of light transmittance or absorbance. 1 – Cells Separate from Plasma 2 – Plasma 3 – Cells Hemostasis Tests Learn about the types of tests performed in the Hemostasis Lab. Slide NumberText BlocksCalloutsAudio ScriptImage File1Welcome to the Virtual Laboratory. Tests performed in the hemostasis laboratory: Prothrombin Time (PT) Activated Partial Thromboplastin Time (APTT) Fibrinogen assay D-dimer Assay Coagulation Factor Assays Platelet Function Assay (PFA) Select Next to continue.Note: If audio does not automatically start, select the play arrow in the top left to begin.Welcome back to the Virtual Laboratory. The hemostasis laboratory plays an important role in diagnosing, monitoring and treatment of bleeding and clotting disorders. Just as there are many interdependent systems to maintain hemostasis within the body, there are many different tests used to monitor the effectiveness of these systems. In this visit, you will learn about some of the most common tests performed in the hemostasis laboratory. 2Prothrombin Time (PT) Evaluates the extrinsic and common pathways Measures the time in seconds to create a fibrin clot Screening test for evaluating a patient's ability or inability to clot Select Next to continue.The Prothrombin Time or PT is used to evaluate the effectiveness of the Extrinsic and Common Pathways of the Coagulation Cascade. It does not test for a specific factor or analyte, but for the ability of all of the factors involved in the extrinsic pathway and common pathway to work together to form a fibrin clot. The test is performed by adding thromboplastin and calcium to the patient’s plasma sample and measuring the amount of time required to form a fibrin clot. The PT and aPTT together are common screening tests when evaluating a patient’s ability to clot especially prior to surgery or other medical procedures. It also is a good starting point when a patient is bleeding for an unknown reason. 3Prothrombin Time (PT) International Normalized Ratio (INR) Used to monitor oral anticoagulant therapy Standardized result regardless of instrument or reagent system used Select Next to continue.The PT also is the test used to monitor oral anticoagulant therapy. The physician uses the result to determine if the patient is taking the appropriate amount of warfarin. Since the PT result in seconds can vary depending on the instrument or reagents used, the PT also is reported out as an INR or International Normalized Ratio. This value is a way to standardize the patient’s PT result, regardless of what laboratory performs the testing.4Activated Partial Thromboplastin Time (APTT) Evaluates the intrinsic and common pathways Measures the time in seconds to create a fibrin clot Screening test for evaluating a patient's ability or inability to clot Used to monitor heparin therapy Select Next to continue.The activated Partial Thromboplastin Time or aPTT is used to evaluate the effectiveness of the Intrinsic and Common Pathways of the Coagulation Cascade. It does not test for a specific factor or analyte, but for the ability of all of the factors involved in the intrinsic pathway and common pathway to work together to form a fibrin clot. During the aPTT test procedure, several reagents are added to the patients sample. An activator is used to simulate the surface contact that initiates the intrinsic pathway. Partial Thromboplastin is used as a platelet substitute and calcium is added. The time until the fibrin clot is formed is reported in seconds. The PT and aPTT together are common screening tests when evaluating a patient’s ability to clot especially prior to surgery or other medical procedures. It provides a good starting point when a patient is bleeding for an unknown reason. The activated Partial Thromboplastin time also is utilized when monitoring heparin therapy. The physician determines the appropriate amount of heparin to give a patient based on the increase in the patient’s aPTT result. 5Fibrinogen Assay Evaluates the amount of fibrinogen capable of converting to fibrin Measures time in seconds required to form a fibrin clot then converts the seconds to a concentration Critical test for determining the severity of DIC (Disseminated Intravascular Coagulation) Select Next to continue.Fibrinogen is the direct precursor to fibrin. When evaluating a patient’s ability to clot, it is important to know how much fibrinogen the patient has to convert to fibrin. Unlike the PT and aPTT assays, the fibrinogen assay specifically measures the amount of active fibrinogen in a sample. The test is performed by adding thrombin to the patient’s sample. Thrombin converts fibrinogen to fibrin and the amount of time required to form a fibrin clot is measured in seconds. Since the physician needs to know the amount of fibrinogen in the sample, the seconds are converted to a concentration. The fibrinogen assay is critical when evaluating the severity of a patient in DIC. During DIC, the patient is clotting uncontrollably and consuming all of the coagulation factors, including fibrinogen. The concentration of fibrinogen left in a patient’s sample allows the physician to assess the severity of the patient’s condition. 6D-dimer Assay Evaluates the presence of D-dimers in the patient sample Turbidity of the test solution is measured and converted to a concentration Concentration of D-dimer in a patient sample can help rule out deep vein thrombosis and pulmonary embolism Select Next to continue.When plasmin breaks down a stable fibrin clot during fibrinolysis, D-dimers are formed. A quantitative D-dimer such as the INNOVANCE™ D-Dimer assay can measure the concentration of these molecules. The reagent used during the D-dimer assay contains latex beads coated with antibodies specific to D-dimer. When D-dimer is present in the patient sample, the latex beads stick together and the turbidity of the solution is measured and converted to a concentration. Since D-dimers are only formed from the cross-linkage fibrin strands when the fibrin clot is stabilized, the detection of D-dimer in the patient sample indicates that a clot has formed and been broken down. This helps the physician diagnose clotting disorders such as Deep Vein Thrombosis or Pulmonar Embolism. 7Factor Assays Evaluates specific factors in the coagulation cascade Sample is added to a reagent plasma deficient in the factor being tested for and either a PT or APTT is measured.  The time required to form the fibrin clot is converted to a % activity Factor assays can be used to determine factor deficiencies such as Hemophilia Select Next to continue.Coagulation factor assays test for specific factors in the coagulation cascade. The patient sample is mixed with a reagent plasma that is deficient in the factor being tested for, such as Factor VIII. This factor VIII deficient plasma contains all the coagulation factors except factor VIII. Since factor VIII is part of the intrinsic pathway, an aPTT is then measured. The time until a fibrin clot is formed is measured and converted to a percent activity level for factor VIII. Factor assays are used to determine factor deficiencies such as the Factor VIII deficiency of Hemophilia patients. 8Platelet Function Assay (PFA) Evaluates the ability of platelets to adhere and aggregate Time required to plug an aperture is measured and reported in seconds Determines platelet dysfunction such as von Willebrands Disease or Aspirin ingestion Select Next to continue.Select each number to review the corresponding text.CalloutsPlatelet ActivationInjured VesseThe Platelet Function Assay or PFA determines the ability of a patients platelets to aggregate during primary hemostasis. During the PFA assay the patient’s whole blood is added to a cartridge coated with reagents. The time required for the platelets to plug a small aperture is measured and reported in seconds. The PFA is used to determine if the patient has a platelet dysfunction such as Von Willebrands Disease or Aspirin Ingestion. 9Congratulations.You now have learned about the tests performed in the hemostasis laboratory.When complete, select the X in the upper-right corner to close the window and continue.Congratulations! You’ve now learned about the tests performed in the hemostasis laboratory.