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Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where they help keep the bite area unclotted long enough for the animal to obtain some blood. As a class of medications, anticoagulants are used in therapy for thrombotic disorders. Oral anticoagulants (OACs) are taken by many people in pill or tablet form, and various intravenous anticoagulant dosage forms are used in hospitals. Some anticoagulants are used in medical equipment, such as sample tubes, blood transfusion bags, heart–lung machines, and dialysis equipment. One of the first anticoagulants, warfarin, was initially approved as a rodenticide.
A thrombus, colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cross-linked fibrin protein. The substance making up a thrombus is sometimes called cruor. A thrombus is a healthy response to injury intended to stop and prevent further bleeding, but can be harmful in thrombosis, when a clot obstructs blood flow through healthy blood vessels in the circulatory system.
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism of coagulation involves activation, adhesion and aggregation of platelets, as well as deposition and maturation of fibrin.
Warfarin is an anticoagulant used as a medication under several brand names including Coumadin. While the drug is described as a "blood thinner", it does not reduce viscosity but rather inhibits coagulation. Accordingly, it is commonly used to prevent blood clots in the circulatory system such as deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who have atrial fibrillation, valvular heart disease, or artificial heart valves. Less commonly, it is used following ST-segment elevation myocardial infarction and orthopedic surgery. It is usually taken by mouth, but may also be administered intravenously.
Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Since heparins depend on the activity of antithrombin, they are considered anticoagulants. Specifically it is also used in the treatment of heart attacks and unstable angina. It is given intravenously or by injection under the skin. Other uses for its anticoagulant properties include inside blood specimen test tubes and kidney dialysis machines.
Antiphospholipid syndrome, or antiphospholipid antibody syndrome, is an autoimmune, hypercoagulable state caused by antiphospholipid antibodies. APS provokes blood clots (thrombosis) in both arteries and veins as well as pregnancy-related complications such as miscarriage, stillbirth, preterm delivery, and severe preeclampsia. Although the exact etiology of APS is still not clear, genetics is believed to play a key role in the development of the disease. The diagnostic criteria require one clinical event and two positive blood test results spaced at least three months apart that detect lupus anticoagulant, anti-apolipoprotein antibodies, or anti-cardiolipin antibodies.
Low-molecular-weight heparin (LMWH) is a class of anticoagulant medications. They are used in the prevention of blood clots and treatment of venous thromboembolism and in the treatment of myocardial infarction.
The prothrombin time (PT) – along with its derived measures of prothrombin ratio (PR) and international normalized ratio (INR) – is an assay for evaluating the extrinsic pathway and common pathway of coagulation. This blood test is also called protime INR and PT/INR. They are used to determine the clotting tendency of blood, in such things as the measure of warfarin dosage, liver damage, and vitamin K status. PT measures the following coagulation factors: I (fibrinogen), II (prothrombin), V (proaccelerin), VII (proconvertin), and X.
The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time, is a blood test that characterizes coagulation of the blood. A historical name for this measure is the kaolin-cephalin clotting time (KCCT), reflecting kaolin and cephalin as materials historically used in the test. Apart from detecting abnormalities in blood clotting, partial thromboplastin time is also used to monitor the treatment effect of heparin, a widely prescribed drug that reduces blood's tendency to clot.
Thromboelastography (TEG) is a method of testing the efficiency of blood coagulation. It is a test mainly used in surgery and anesthesiology, although increasingly used in resuscitations in emergency departments, intensive care units, and labor and delivery suites. More common tests of blood coagulation include prothrombin time (PT) and partial thromboplastin time (aPTT) which measure coagulation factor function, but TEG also can assess platelet function, clot strength, and fibrinolysis which these other tests cannot.
Warfarin-induced skin necrosis is a condition in which skin and subcutaneous tissue necrosis occurs due to acquired protein C deficiency following treatment with anti-vitamin K anticoagulants.
Phenprocoumon is a long-acting blood thinner drug to be taken by mouth, and a derivative of coumarin. It acts as a vitamin K antagonist and inhibits blood clotting (coagulation) by blocking synthesis of coagulation factors II, VII, IX and X. It is used for the prophylaxis and treatment of thromboembolic disorders such as heart attacks and pulmonary (lung) embolism. The most common adverse effect is bleeding. The drug interacts with a large number of other medications, including aspirin and St John's Wort. It is the standard coumarin used in Germany, Austria, and other European countries.
The thrombin time (TT), also known as the thrombin clotting time (TCT), is a blood test that measures the time it takes for a clot to form in the plasma of a blood sample containing anticoagulant, after an excess of thrombin has been added. It is used to diagnose blood coagulation disorders and to assess the effectiveness of fibrinolytic therapy. This test is repeated with pooled plasma from normal patients. The difference in time between the test and the 'normal' indicates an abnormality in the conversion of fibrinogen to fibrin, an insoluble protein.
Ecarin clotting time (ECT) is a laboratory test used to monitor anticoagulation during treatment with hirudin, an anticoagulant medication which was originally isolated from leech saliva. Ecarin, the primary reagent in this assay, is derived from the venom of the saw-scaled viper, Echis carinatus.
Hypercoagulability in pregnancy is the propensity of pregnant women to develop thrombosis. Pregnancy itself is a factor of hypercoagulability, as a physiologically adaptive mechanism to prevent post partum bleeding. However, when combined with an additional underlying hypercoagulable states, the risk of thrombosis or embolism may become substantial.
Direct factor Xa inhibitors (xabans) are anticoagulants, used to both treat and prevent blood clots in veins, and prevent stroke and embolism in people with atrial fibrillation (AF).
Thromboelastometry (TEM), previously named rotational thromboelastography (ROTEG) or rotational thromboelastometry (ROTEM), is an established viscoelastic method for hemostasis testing in whole blood. It is a modification of traditional thromboelastography (TEG).
Direct thrombin inhibitors (DTIs) are a class of anticoagulant drugs that can be used to prevent and treat embolisms and blood clots caused by various diseases. They inhibit thrombin, a serine protease which affects the coagulation cascade in many ways. DTIs have undergone rapid development since the 90's. With technological advances in genetic engineering the production of recombinant hirudin was made possible which opened the door to this new group of drugs. Before the use of DTIs the therapy and prophylaxis for anticoagulation had stayed the same for over 50 years with the use of heparin derivatives and warfarin which have some well known disadvantages. DTIs are still under development, but the research focus has shifted towards factor Xa inhibitors, or even dual thrombin and fXa inhibitors that have a broader mechanism of action by both inhibiting factor IIa (thrombin) and Xa. A recent review of patents and literature on thrombin inhibitors has demonstrated that the development of allosteric and multi-mechanism inhibitors might lead the way to a safer anticoagulant.
Kaolin clotting time (KCT) is a sensitive test to detect lupus anticoagulants. There is evidence that suggests it is the most sensitive test for detecting lupus anticoagulants. It can also detect factor VIII inhibitors but is sensitive to unfractionated heparin as well.
The haemostatic system involves the interaction of proteins in the blood, the blood vessel wall and the flow of blood to control bleeding and blood clotting. Developmental Haemostasis is a term that represents the maturation of the haemostatic system from birth to adulthood. There are differences in the concentration, structure and activity of many proteins involved in blood clotting. These changes play an important role in physiological development and are important in providing appropriate diagnosis and treatment of bleeding and clotting disorders. The age-specific differences in the blood clotting system may contribute to the fact that children are less prone to developing thrombosis compared to adults.
References
- ↑ Horton, S; Augustin, S (2013), "Activated Clotting Time (ACT)", Haemostasis, Methods Mol Biol, vol. 992, pp. 155–167, doi:10.1007/978-1-62703-339-8_12, ISBN 978-1-62703-338-1, PMID 23546712.
- 1 2 3 labtestsonline.org > ACT This article was last reviewed on March 20, 2008. This page was last modified on March 30, 2010
- ↑ Searles, Bruce (March 2006). "Urban Myths and the ACT: What is Not True and What Really Matters When it Comesto Monitoring Anticoagulation". The Journal of Extra-corporeal Technology. 38 (1): 56–58. ISSN 0022-1058. PMC 4680769 . PMID 16637527.
- ↑ "Coagulation Monitoring" (PDF). Archived (PDF) from the original on 2017-08-29. Retrieved 2021-03-17.
- ↑ Ojito, Jorge W.; Hannan, Robert L.; Burgos, Michelle Moore; Lim, Hyunsoo; Huynh, Monique; Velis, Evelio; Arocha, Marino; Tirotta, Christopher F.; Burke, Redmond P. (March 2012). "Comparison of Point-of-Care Activated Clotting Time Systems Utilized in a Single Pediatric Institution". The Journal of Extra-corporeal Technology. 44 (1): 15–20. ISSN 0022-1058. PMC 4557434 . PMID 22730859.
- ↑ "I-Stat Technical Bulletin: calibration options" (PDF). Retrieved 2021-03-18.
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