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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