Tests for hemostasis and their relevance to venous thrombosis

The authors have tried to determine which patients were at risk of venous thrombosis. They chose 10 tests for hemostasis that might be of value in predicting those patients who were at risk. The tests were used in two groups of patients: one group in a respiratory intensive care unit and another group of patients about to undergo a major spinal operation. The tests were those for measuring: platelet count, prothrombin time, activated partial thromboplastin time, platelet thromboplastic activity (platelet factor 3), plasma clotting time, and concentrations of fibrinogen, plasminogen, antithrombin-III, alpha-1-antitrypsin and platelet fibrin degradation products (FDP). A diagnosis of thrombosis was made by three techniques: radioactive fibrinogen accumulation in the developing thrombus, impedance plethysmograhpy and ascending venography. The only test for hemostasis that discriminated between patients with and without thrombosis was the level of circulatory FDP. Several of the tests showed pronounced changes within the normal range following development of thrombosis and even before its detection. Therefore, none of the tests was truly predictive. A detailed discussion of the performance and interpretation of impedance plethysmography is presented.