Hemostasis

HEMOSTASIS Definition the collective term for all the physiologic mechanisms the body uses to protect itself from blood loss http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/tr/m1/s7/trm1s7_3.htm

HEMOSTASIS Complexity It is the process by which the body simultaneously stops bleeding from an injured site yet maintains blood in the fluid state within the vascular compartment.

BRUISES Petechia < 2 mm Purpura 2 mm – 10 mm Ecchymosis >10 mm

PETECHIA Less than 2-mm in diameter

ECCHYMOSIS Greater than 1- cm in diameter

HEMOSTASIS Components Vascular system Platelets Smooth muscle contractions Platelets Number and function Tissue and circulating proteins (coagulation factors) Presence and function

VASCULAR SYSTEM Smooth muscle action Activated by trauma Smooth muscles in the walls of small arterial structures (arterioles and smaller)will contract and stop leakage

Platelets Measured Platelet count Estimated Blood smear

PLATELETS Platelet count Reference range 150,000 to 400,000/ul of blood < 100,000 = Thrombocytopenia 20,000 – 50,000 are associated with post traumatic bleeding <20,000 spontaneous bleeding becomes evident platelet count can be adequate, but the function may be impaired Perform function tests if suspicious of impairment in function

Platelets The large cell shown on the next slide, the megakaryocyte, stays in the bone marrow after it differentiates from the stem cell. Megakaryocytes are like factories. They manufacture and shed millions of little pieces of themselves into the blood. These pieces of cell, called platelets, contain the substances necessary to help blood clot.

The Coagulation Process

PLATELETS Function To begin the process of clotting by sticking to exposed collagen fibers in the lining of vessels To cause aggregation of groups of platelets to form a plug Release of platelet factor 3 to start the intrinsic coagulation cascade

PLATELET Go online and search for an electron microscope image of a platelet, the ones that pigmented blood elements are especially neat

Coagulation Factor Testing

Intrinsic Pathway

Partial Thromboplastin Time AKA: Activated Partial Thromboplastin Time; aPTT; APTT Evaluates the coagulation factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen) as well as prekallikrein (PK) and high molecular weight kininogen (HK). Surface activation factors are added to the plasma sample and a clot forms This is timed

Extrinsic Pathway

Prothrombin Time AKA Pro Time; Protime Evaluates the coagulation factors VII, X, V, II, and I (fibrinogen). Tissue activation factors are added to the plasma sample and a clot forms This is timed

Common Pathway

Thrombin Time AKA: TT; Thrombin Clotting Time Prolongation of TT may indicate decreased fibrinogen level (hypofibrinogenemia or afibrinogenemia) and/or abnormal function of fibrinogen (dysfibrinogenemia). The clotting-based, functional fibrinogen assay is now routinely available in clinical laboratories and has largely replaced the need for TT for evaluation of fibrinogen. Thrombin is added to the plasma sample and a clot forms This is timed

Interpretation of PT and PTT in Patients with a Bleeding or Clotting Syndrome PT result PTT result Common condition present Prolonged Normal Liver disease, decreased vitamin K, decreased or defective factor VII Decreased or defective factor VIII, IX, or XI, von Willebrand disease, or lupus anticoagulant present Decreased or defective factor I, II, V or X, severe liver disease, disseminated intravascular coagulation (DIC) Normal or slightly prolonged May indicate normal hemostasis; however PT and PTT can be normal in conditions such as mild deficiencies in other factors and mild form of von Willebrand disease. Further testing may be required to diagnose these conditions. Labtestsonline.org

Fibrinogen This is a zymogen that activates to become fibrin following stimulation by thrombin It is a non-specific, acute phase, reactant Decreased levels might indicate: Bleeding disorder Elevated levels might indicate: Acute infections Cancer Coronary heart disease, Myocardial infarction Stroke Inflammatory disorders (like rheumatoid arthritis and glomerulonephritis) Trauma

Plasma Fibrinogen Plasma fibrinogen levels can also be measured If this level is low then all times would be increased

Fibrinolysis Clot removal following repair Plasmin Activated enzyme from the zymogen plasminogen that digests fibrin and also removes fibrinogen from circulation so more fibrin won’t form Specific tissue activator is released from the site of the blood clot that forms a type of plasmin which removes the fibrin but leaves the fibrinogen alone

Antiphospholipid syndrome The Lancet, Volume 376, Issue 9751, Pages 1498-1509 Guillermo Ruiz-Irastorza, Mark Crowther, Ware Branch, Munther A Khamashta

Screening Tests Do they bleed to much?

Viscoelastometry Blood clots have to be strong to stop bleeding and prevent new bleeding until healing can occur. This type of testing is designed to determine the strength of a blood clot as it forms. Substances are added to blood to start clotting while clot strength is being measured over time. Measurements are made of total clot strength, time to reach maximum strength, and loss of strength over time. These tests may be abnormal if the platelet count is low, if platelet function is reduced, or if anti-platelet medications are present. This type of testing is most often performed in larger hospitals either in the operating room as a point-of-care test or in the clinical laboratory.

Closure time assays In this test, blood is exposed to various substances that activate platelets. The blood is then drawn through a simulated wound, a small hole in a tiny tube that is coated with collagen, a protein that promotes platelet binding to wounds. In normal blood, activated platelets will bind to the coated hole, eventually plugging it. The time required to plug the hole is measured. This is called the closure time. The longer the closure time, the lower the platelet function. This test may be abnormal if the platelet count is low, if platelet function is reduced, if other proteins needed for platelet function are reduced or if anti-platelet medications are present. This type of assay can be used to screen for von Willebrand disease and some platelet function disorders, but it will not detect all platelet function disorders, particularly the milder forms. This test is relatively simple to perform and is available in many health care facilities.

Bleeding time In the past, the primary screen for platelet dysfunction was the bleeding time – a test that involved making two small, shallow, standardized cuts on the inner forearm and measuring the amount of time that they took to stop bleeding. The bleeding time procedure has fallen from favor in recent years. Many hospitals are no longer offering it, and several national organizations have issued position statements against its routine use. The bleeding time is not sensitive or specific, and it does not necessarily reflect the risk or severity of surgical bleeding. It is poorly reproducible, can be affected by aspirin ingestion and by the skill of the person performing the test, and frequently leaves small thin scars on the forearm.

Diagnostic Tests Why do they bleed too much?

Platelet aggregometry Many different substances can activate a platelet, including proteins in the wound, factors released from other activated platelets, and factors produced by the coagulation system that aids platelets in forming a strong plug to stop bleeding. Many different platelet abnormalities have been described due to problems with one or more of these activating systems. Platelet aggregometry consists of 4 to 8 separate tests. In each test, a different platelet activating substance is added to blood, followed by measurement of platelet aggregation over several minutes. When complete, a physician reviews and interprets the entire panel of tests to determine if there is any evidence of abnormal platelet function. Platelet aggregation testing can diagnose a variety of inherited and acquired platelet function disorders. It is typically performed at academic medical centers or large hospitals due to the complexity of the testing and interpretation.

Flow cytometry Platelets can be evaluated for functional defects using flow cytometry. This test uses lasers to determine proteins that are present on the platelet surface and how they change when the platelet is activated. Platelet flow cytometry is a highly specialized procedure available only in few reference laboratories to diagnose inherited platelet function disorders.

Conditions

DIFFERENTIAL DX Categories of Bleeding disorders Vascular defects Platelet defects Coagulation defects

Capillary Fragility Tests for fragile capillaries which could indicate a metabolic problem (decreased Vit. C) Procedure B/P cuff @ 80mm/Hg for 5 min and look for petechia

Inherited Platelet Disorders Von Willebrand disease — associated with decreased production or dysfunction of von Willebrand factor and results in reduced platelet adherence to the injured blood vessel and increased blood loss Glanzmann's thrombasthenia — affects platelets ability to aggregate Bernard-Soulier syndrome — characterized by reduced platelet adhesion Storage pool disease — can affect platelet ability to release substances that promote aggregation

Von Willebrand’s Most common inherited bleeding disorder 1 in 100-1000 people Males and females 3 types, generally mild symptoms 1 = low levels of VWfactor 2 = qualitative problems with VWfactor 3 = no VWfactor

Acquired Platelet Disorders Kidney failure (uremia) Myeloproliferative disorders (MPDS) Acute leukemia Medications aspirin and nonsteroidal anti-inflammatory drugs

Inherited & acquired factor deficiencies PTT Prolonged PTTs due to a factor deficiency usually "correct" after being mixed with pooled normal plasma. The PTT may be prolonged in von Willebrand disease, the most common, inherited bleeding disorder, which affects platelet function due to decreased von Willebrand factor. Hemophilia A (VIII) and Hemophilia B (IX)

Hemophilia A = Deficiency in factor VIII B = Deficiency in factor IX Symptoms of both A & B Bleeding into joints, with associated pain and swelling Blood in the urine or stool Bruising Gastrointestinal tract and urinary tract hemorrhage Prolonged bleeding from cuts, tooth extraction, and surgery Spontaneous bleeding Nosebleeds

Inherited & acquired factor deficiencies PT Liver disease, decreased vitamin K, decreased or defective factor VII Deficiency of vitamin K. Extremely poor diet, malabsorption, antibiotic use, liver disease, can be causative Decreased or defective factor I, II, V or X, severe liver disease, disseminated intravascular coagulation (DIC)