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Coagulation
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Coagulation Hemostasis is the cessation of blood flow from an injured blood vessel. It is one of the most important natural defense mechanisms of the body. The process of hemostasis involves numerous interdependent "coagulation factors" that are controlled carefully by the body for the purpose of preventing bleeding. When there is an injury to a blood vessel, the hemostatic process is designed to repair the break. Thus, "hemostasis" is the process whereby the body retains blood within the vascular system, in spite of the many traumas that injure the blood vessel walls.
The most immediate response to blood vessel injury is "vasoconstriction". This is where the blood vessel constricts, decreasing the blood flow through the injured area. A platelet plug can then form, which helps to further inhibit the bleeding. Finally, the "coagulation factors" present in the blood interact, forming a clot, to stop the bleeding completely.
Platelets are a type of blood cell which travels throughout your blood stream. (Refer to Hematology Page.) "Coagulation factors" are chemicals (protein, calcium, and phospholipid) that are found in your blood. There are quite a few of these special "coagulation factors" and they have been assigned Roman numeral (Factor I through Factor XIII).
The coagulation laboratory performs tests which will assess your platelet function and assess the activity of your coagulation factors. Your physician will frequently use the coagulation laboratory to help diagnosis such disease states as hemophilia A, hemophilia B and Von Willebrand's disease. Or she may use it to monitor your heparin or coumadin (blood thinners) therapy.
Crestwood Medical Center is proud to offer to the online community a database of some of the tests performed by the coagulation laboratory. In order to access this information, simply page down. Please bookmark our page for easier access.
THE PROTHROMBIN TIME TEST
Normal Range = 11.0 - 13.5 seconds T he prothrombin time (PT) is used to test for factor deficiencies in the extrinsic coagulation pathway. Prolongation of the PT will be observed in factors 2, 5, 7, 10 and fibrinogen deficiency. The PT will also be prolonged in liver disease, and vitamin K deficiency .It is also used to monitor the effects of blood thinners.
If you are at risk for blood clotting, your physician may put you on a "blood thinner" like Coumadin. And he will want to make sure that you are getting enough medication to "thin" your blood appropriately. This will decrease the likelihood that you will form a blood clot that may travel to a vital organ. However, it is very important that you are not getting too much medication because it may cause bleeding. There is a very delicate balance here. This test is used to monitor your clotting time to make sure that you are getting just the right dosage. If the clotting test is too prolonged the doctor will respond by decreasing your dosage. On the other hand, if the clotting test is not prolonged enough, he will increase your Coumadin.
THE ACTIVATED PARTIAL THROMBOPLASTIN TIME TEST
Normal Range = 25.0-35.0 seconds T he activated partial thromboplastin time, or PTT, is used to test for factor deficiencies in the extrinsic coagulation pathway. Prolongation of the aPTT will be observed in factors 2, 5, 8, 9, 10, 11, 12 and/or fibrinogen deficiency. The aPTT will also be prolonged in patients receiving heparin therapy, another type blood thinner.
THE BLEEDING TIME TEST
Normal Range = 3.5 - 12.0 minutes T he bleeding time is a test that evaluates platelet function. It is performed by making a small cut on your arm with a small sterile blade and measuring the time it takes for the wound to stop bleeding. The bleeding time will be prolonged in patients taking aspirin (a blood thinner that works by affecting the function of platelets, patients with On Willebrand's Disease, and in patients with low platelet counts and patients with nonfunctional platelets.
FIBRINOGEN
Fibrinogen is a soluble plasma protein that when acted on by the enzyme thrombin results in a fibrin clot. The fibrinogen my be decreased in massive bleeding and in disease states such as afibrinogemia.
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