Thursday, March 19, 2015

Partial Thromboplastin Time


Patient's plasma is activated to clot in vitro by mixing it with phospholipid and an activator substance. Screens the intrinsic coagulation pathway and adequacy of all coagulation factors except XIII and VII. PTT is usually abnormal if level of any factor falls below 30-40% of normal. 


Normal Range: 25-35 (range varies) Panic > = 60 seconds

increased in: Deficiency of any individual coagulation factor except XIII and VII, nonspecific inhibitors (lupus-like anticoagulant), specific factor inhibitors, von Willebrand's disease (may also be normal), hemophilia A and B, disseminated intravascular coagulation. Drugs: heparin, warfarin. 
Decreased in: Hypercoagulable states, DIC. 
 
Comments: PTT is the best test to monitor adequacy of heparin therapy. Test not always abnormal in von Willebrand's disease. Test may be normal in chronic DIC. Very common cause of prolongation is spurious presence of heparin in sample. 

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