- Hemostasis constitutes a number of processes which guard the body against blood loss.
- Injury to the blood vessel wall sets in motion complex phenomena which involve blood platelets (activation, adhesion, aggregation), and a cascade of coagulation factors, classified into intrinsic, extrinsic and final common pathways.
- The integrity of these three systems may be tested by simple laboratory tests.
- Deficiencies of factors participating in the coagulation cascade, and/or disordered platelet function, result in bleeding disorders.
- Eventually, blood clots are degraded by the fibrinolytic system. The process of fibrinolysis prevents thrombotic phenomena and there is normally a balance between hemostasis and thrombosis.
- Aspirin
 , and clot dissolution using intravenous infusion of enzymes such as streptokinase, are now established treatments for acute myocardial infarction. - Aspirin (or other antiplatelet agents) are also used to reduce risk of recurrent myocardial infarction and stroke.
- Anticoagulant drugs (heparin then warfarin) are used in treatment of acute venous thrombosis or embolism.
- Anticoagulant drugs (warfarin) are used long-term to prevent thromboembolism from the heart (atrial fibrillation, heart valve prostheses).
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Test your knowledge:
- When a patient presents with excessive bleeding from multiple sites, what laboratory tests should be done to identify the likely cause of their hemostatic defect?
- When a patient presents with a painful swollen leg, possibly due to acute deep venous thrombosis (DVT), what laboratory tests can be performed to help the clinician:
- to establish or exclude this diagnosis?
- to monitor anticoagulant treatment, after the diagnosis has been confirmed?
- When a patient presents with acute coronary artery thrombosis (evolving to myocardial infarction), what antithrombotic drugs should be urgently considered to reduce the risk of complications?
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