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===BMBT===
===BMBT===
Bleeding Time
Definition
When a small slit is made in the skin, the hemostatic mechanisms necessary for coagulation are activated. Without the aid of external pressure, bleeding usually stops within 7 to 9 minutes.
Technique
The test is performed using a disposable template that produces a uniform incision. The incision, either horizontal or vertical, is placed on the lateral aspect of the forearm, about 5 cm below the antecubital fossa, after a blood pressure cuff has been inflated to approximately 40 mm Hg. Blood may be absorbed off the skin, but care must be taken to avoid pressure. The time is measured from the moment of incision to the moment bleeding stops. The time may vary based on the commercial template used, the direction of the incision, and the location on the arm. Each institution must establish its own upper limits of normal.
Basic Science
The vascular platelet phase of hemostasis consists of a primary vasoconstriction that serves to decrease blood flow, followed by adherence of platelets to the ruptured endothelium (adhesion) and each other (aggregation). This platelet aggregate, called the platelet plug, stops the bleeding and forms a matrix for the clot. The bleeding time is an excellent screening test for the vascular platelet phase of hemostasis. It depends on an intact vasospastic response in a small vessel and an adequate number of functionally active platelets.
Clinical Significance
Patients with abnormalities of the vascular platelet phase of hemostasis present with purpura (petechiae and ecchymoses) and spontaneous bruising. They may have mucosal bleeding and fundus hemorrhages. Commonly, the problem is either thrombocytopenia, easily evaluated by a platelet count, or abnormal platelet function, which can be diagnosed with platelet function studies. The most common acquired platelet function abnormalities are drug induced (aspirin and the nonsteroidal anti-inflammatory agents) and uremia. The most common hereditary abnormality is von Willebrand's disease.
==Tests Evaluating Secondary Haemostasis==
==Tests Evaluating Secondary Haemostasis==