Platelet thromboplastin

The antihemophilic globulin, the factor absent from the blood in the best-known hemophilia, combines stoichiometrically with a platelet thromboplastic factor, and the two compounds act like precursors, yielding a product itself a precursor. For thromboplastin, the product is prothromboplastin. The platelet thromboplastin component acts like a catalyst consequently, its concentration does not change during the reaction. The prothromboplastin combines with another compound called the plasma-accelerating globulin to yield a new product, namely, thromboplastin. 

Thus, if the water-soluble fraction is absorbed on tricalcium phosphate and then centrifuged, the supernatant contains a platelet factor referred to as factor I. The tricalcium phosphate pellet contains another factor called factor II, which can be eluted with 0.2% m sodium citrate. Factor II accelerates the conversion of fibrinogen to fibrin by thrombin. Factor III has thromboplastic activity and reverses the anticoagulant effect of heparin, and platelet thromboplastin, or factor IV, reacts with plasma components on active thromboplastin. At least two other factors have been described in platelets—serotonin and fibrinogen that coagulates under the influence of thrombin. Available evidence suggests that fibrinogens in plasma and pate-lets are identical. 

Hematological Effects. Leukocytosis and decreased platelet counts were reported in a group of subjects shortly after they ingested an unknown amount of endosulfan (Blanco-Coronado et al. 1992). One subject from that study, who eventually died, had prolonged partial thromboplastin time and prothrombin time with thrombocytopenia, and decreased fibrinogen two days after being admitted to the hospital. Elevated white cell count was also observed in an additional case of fatal acute poisoning with... 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Anticoagulant or heparin use <48 h before onset with elevated partial-thromboplastin time Prothrombin time >15 s Platelet count <100,000/mm ... 

Monitor the following serial laboratories for comparison to baseline values every 6 hours in the first 24 hours and daily thereafter until normalized sodium, serum creatinine, blood urea nitrogen, serum lactate, glucose, bilirubin, hemoglobin, hematocrit, platelets, prothrombin time, partial thromboplastin time, arterial blood gases, and pH. 

In a patient presenting with a bleeding or clotting disorder, an initial evaluation should include bleeding time, prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time, and platelet count. 

Increased prothrombin time, partial thromboplastin time, platelet aggregation time, platelet count, and factors II, VII, VIII, IX, X, XII, Vll-X complex, ll-VII-X complex, and -thromboglobulin decreased antithrombin III, antifactor Xa increased fibrinogen, plasminogen, norepinephrine-induced platelet aggregability. 

Note ACE = angiotensin-converting enzyme INR = international normalized ratio PT = prothrombin time PTT = partial thromboplastin time ECG = electrocardiogram PAF = platelet-activating factor AUC = area under the concentration/time curve. 

Hageman factor (XII), antihemophilic globulin (VIII), Christmas factor (IX), plasma thromboplastin antecedent (XI), calcium (IV), and platelet phospholipids... 

Abbreviations aPTT, activated partial thromboplastin time AT, antithrombin HC, heparin cofactor HIT, heparin-induced thrombocytopenia PCI, percutaneous coronary intervention PF, platelet factor UFH, unfractionated heparin. 

Clinical Examination A detailed clinical examination should include the following hematology including hematocrit, hemoglobin concentration, erythrocyte count, total and differential leukocyte counts, measure of clotting potential, (e.g., clotting time, prothrombin time, thromboplastin time, platelet count). These evaluations should be performed at the end of the test period. 

Haematopoietic Blood tests Complete blood count (red and white blood cell indices and platelets) measurement of clotting factors, prothrombin time, partial thromboplastin time... 

A 47-year-old woman who had had bilateral mastectomies for breast cancer became depressed and was given paroxetine 20 mg/day. After 15 days she developed widespread multiple ecchymoses over the arms, legs, and abdomen. Her platelet count, prothrombin time, partial thromboplastin time, and bleeding time were normal. Paroxetine was withdrawn, and 5 days later, the bruising had markedly abated and no new... 

Exogenous activation is initiated by tissue thromboplastin (= tissue factor) and the activated form of factor XII in the plasma. This complex is enlarged by ionic calcium and platelet factor 3. As a result, the activation of factors IX to IXa and X to Xa is triggered, thus forming a cross-connection between the endogenous and the exogenous system, (s. fig. 19.1)... 

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