Lecture_Three - Class Notes-Lecture Three Tests of clotting...

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Class Notes-Lecture Three Tests of clotting function Remember from anatomy and physiology some of the factors responsible for hemostasis like prothrombin, thrombin, fibrinogen, fibrin, vitamin K, clotting factors, and platelet. The liver plays an important role in the synthesis of plasma proteins like prothrombin. Also, bile salts from the liver are necessary for efficient absorption of vitamin K from the gut. For this reason, patients with abnormal liver function may also have coagulation disorders. Coagulation disorders fall into two main groups--those that result in excessive bleeding and those that produce abnormal clotting. Several tests are available to determine the nature and extent of coagulation (hemostasis) disorders. We will focus on some of the most common such as: Platelelets: Normal value 130,000 to 360,000/mm3. Produced in the red bone marrow, they are also called thrombocytes, thus the term thrombocytopenia (a platelet count less than normal) or thrombocytosis (a platelet count above the normal range). Platelets play an important role in helping to close breaks in damaged blood vessels. They also release serotonin which causes smooth muscles within the vessel walls to constrict. Panic value is <20,000 mm3 Bleeding time: Normal value 3-10 minutes. A small stab wound is made in either the ear lobe or the forearm. The bleeding time is measured. The length of bleeding depends upon the quality and quantity of plateletes and the ability of the blood vessel to constrict. Focus is on platelet function. Partial thromboplastin time (PTT); Activated Partial thromboplastin time (APTT): Normal value PTT: 30-45 seconds, APTT: 16-25 seconds, an APTT > 100 seconds signifies spontaneous bleeding. The PTT test is used when someone has unexplained bleeding or clotting. The PTT is often used as a starting place when investigating the cause of a bleeding or thrombotic episode. The PTT evaluates deficiencies in components of the intrinsic clotting system. It is often used with recurrent miscarriages that often are associated with anticardiolipin and phospholipid antibodies. The PTT and PT tests are also sometimes used as pre-surgical screens for bleeding tendencies, although numerous studies have shown that they are not useful for this purpose. The PTT is also used to monitor heparin anticoagulant therapy as well as other therapeutic anticoagulants such as hirudin or argatroban. These are substitute drugs that may be used when a patient has heparin-induced thrombocytopenia, which is a decreased platelet count. If the PTT is prolonged, and the cause is not due to heparin contamination or to other pre-analytical problems such as an insufficient or clotted blood sample, then the PTT is followed by mixing studies to check for possible factor deficiencies or inhibitors. Mixing is a procedure where the patient’s plasma is mixed with pooled normal plasma (a combination of blood from different donors that has normal amounts of all of the clotting factors in it). If the patient has a factor deficiency,
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This note was uploaded on 02/29/2012 for the course HEALTH SCI 101 taught by Professor Lesliehangman during the Fall '11 term at Boise State.

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Lecture_Three - Class Notes-Lecture Three Tests of clotting...

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