- PTT is tested by adding substances to a sample of the patient's plasma to initiate the clotting system and determine the time for a clot to form. This procedure is particularly useful in evaluating the intrinsic clotting system.
- PTT may be increased when there is a deficiency or inhibition of any coagulation factors (with the exception of factors XIII and VII), in von Willebrand disease, hemophilia A, hemophilia B, disseminated intravascular coagulation and in the presence of certain anticoagulant drugs such as heparin or warfarin. PTT may also be increased in leukemia.
- PTT may be decreased when there are abnormally high levels of coagulation factor VIII. This is referred to as a hypercoagulable state or an acute phase reaction.
- Heparin is an anticoagulant drug that has an adverse effect of excessive bleeding. Thus, heparin therapy is often monitored using PTT.
- Other laboratory measures used in the evaluation of blood clotting are: prothrombin time, bleeding time, platelet count, thrombin clotting time, fibrin degradation products level, D-dimer level, coagulation factor levels, and screening for factor inhibitors.
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