Prothrombin Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Prothrombin and links to relevant pages within the course.
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| Match the clotting factor with its commonly associated name: | View Page |
| Factor V is primarily involved in: | View Page |
| Match Factors with the assays used to monitor them | View Page |
| Secondary Hemostasis – The Extrinsic Pathway Functional control of the extrinsic pathway is mediated by Tissue Factor Pathway Inhibitor (TFPI) which binds to and inhibits factor X. Remember, for hemostatic processes to continue, factor VIIa must be able to promote the chemical conversion of factor X into factor Xa. TFPI effectively blocks this action, thereby controlling the initiation of the common pathway. The Prothrombin time (PT) is used to monitor the extrinsic pathway, and the activity of oral anticoagulants such as Coumarin. | View Page |
| Secondary Hemostasis – The Common Pathway Activated factor X (Xa), in the presence of factor V (necessary cofactor), ionized calcium, and platelet factor act to convert prothrombin (precursor) to its active form, thrombin, by cleaving the prothrombin molecule. | View Page |
| Secondary Hemostasis – The Common Pathway Thrombin, after its conversion from prothrombin, catalyzes the conversion of fibrinogen into a fibrin monomer. Additionally, thrombin triggers the conversion of factor XIII into factor XIIIa which forms covalent bonds that crosslink and stabilize the fibrin monomers. Finally, thrombin feeds back into the intrinsic and common pathways, accelerating the action of factors XI, V, and VIII. | View Page |
| Laboratory Tests of Hemostatic Function – Prothrombin Time The prothrombin time is a screening test that helps to assess the functionality of both the extrinsic and common pathways. The effectiveness and presence of factors I, II, V, VII, and X are assayed in this diagnostic test, as they are all found in the aforementioned pathways. The results of the prothrombin time are used in conjunction with other diagnostic tests, as well as the clinical picture of the patient, to determine any hemostatic abnormalities which may be present. In addition to being an integral part of the coagulation disorder assessment process, the PT is also used to determine therapeutic effectiveness of oral anticoagulants, by monitoring drugs such as Warfarin, Coumarin, and Dicoumarol. Prothrombin time test results are reported as the number of seconds needed for a clot to form in the patient specimen using the laboratory's instrument/reagent system, and as the International Normalized Ratio (INR). | View Page |
| Laboratory Tests of Hemostatic Function – Prothrombin Time The INR component of the laboratory result is a calculated value that is used by the clinician to monitor anticoagulant therapy and adjust dosage as dictated by clinical status. An INR of 2.0 - 3.0 is often desired as the therapeutic range. The following formula is used by the clinical laboratory to derive an INR value. The INR must be adjusted for every new lot of PT reagent. INR= (PT of patient/PT of geometric mean of the normal population)ISI The International Sensitivity Index, or ISI value, is provided by the reagent manufacturer as the relative sensitivity of the reagent itself. The INR is used to standardize PT results, and in turn, anticoagulant therapy, across laboratory instrumentation, methodologies, and locale. Be sure to frequently check that ISI values match those of the lot currently in use as erroneous results may otherwise occur . | View Page |
| Anticoagulation Therapy - Oral Anticoagulant Therapy The therapeutic use of oral anticoagulants is typically the long-term solution for the patient in terms of managing situations of thrombosis. Warfarin, a dicumarol derivative, is one of the most popular oral anticoagulants used today. While heparin is administered intravenously and acts to inhibit thrombin, warfarin is given orally, taken in pill form, and functions as a Vitamin K antagonist. In earlier discussions, it was mentioned that certain clotting factors are considered to be vitamin K dependant. They require vitamin K molecules for their action to occur. Vitamin K dependant factors include factor II, VII, IX, and X. Vitamin K dependant metabolic processes involved with these coagulation factors are inhibited by drugs such as warfarin. The chemical structure of warfarin and similar anticoagulants enables them to bind competitively with free vitamin K. The prothrombin time (PT/INR) is used to monitor oral anticoagulant therapy. | View Page |
| Types of Medical Errors
Medical errors usually belong to one or more of these categories: | View Page |
| Alternative to TDM Some drugs are more efficiently monitored by determining their effects rather than by measuring the serum drug level. Warfarin dosing, for example, is better monitored by measuring the Prothrombin time (PT) and International Normalized Ratio (INR). | View Page |